linux 驅動之LCD驅動(有framebuffer)

本文轉載自查看原文 2018-03-17 15:20 1182 Linux 設備驅動

<簡介>

LCD驅動里有個很重要的概念叫幀緩沖(framebuffer)，它是Linux系統為顯示設備提供的一個接口，應用程序在圖形模式允許對顯示緩沖區進行讀寫操作。用戶根本不用關心物理顯示緩沖區的具體位置及存放方式，因為這些都由緩沖區設備驅動完成了。

啟動開發板后執行ls /dev/fb* 命令可以看到，幀緩沖設備的主設備號為29，對應/dev/fbn設備文件，一般為/dev/fb0

在弄清楚LCD驅動架構之前，我們先弄清楚幾個重要的結構體，為了減短篇幅，有一些不是很重要的成員會用省略，具體的源代碼請大家參考Linux源代碼，這里我使用的源代碼是天嵌公司提供的移植好的Linux-2.6.30.4。

a:內核中結構fb_info

fb_info結構體（在include/linux/fb.h文件里定義）

struct fb_info {
int node; /* 序號索引值，/dev/fb0，/dev/fb1 其中0,1 就是從這里獲得的*/
int flags;
struct mutex lock;/* 一般在 open/release/ioctl 函數里會用到的鎖 */
struct fb_var_screeninfo var;/* 可變參數，很重要 */
struct fb_fix_screeninfo fix; /* 固定參數，很重要 */
struct fb_monspecs monspecs;/* Current Monitor specs */
struct work_struct queue; /* Framebuffer event queue */
struct fb_pixmap pixmap; /* Image hardware mapper */
struct fb_pixmap sprite; /* Cursor hardware mapper */
struct fb_cmap cmap; /* Current cmap */
struct list_head modelist; /* mode list */
struct fb_videomode *mode;/* current mode */

。。。。。。

struct fb_ops *fbops;
struct device *device;/* This is the parent */
struct device *dev;/* This is this fb device */

。。。。。。
char __iomem *screen_base;/* "顯存“的基地址 */
unsigned long screen_size; /* ”顯存“的大小 */
void *pseudo_palette; /* 16位假的調色板 */
#define FBINFO_STATE_RUNNING0
#define FBINFO_STATE_SUSPENDED1
u32 state; /* Hardware state i.e suspend */
void *fbcon_par; /* fbcon use-only private area */
/* From here on everything is device dependent */
void *par; /* 這個用來存放私有數據 */
};

a:內核數據結構

fb_ops結構體（在include/linux/fb.h文件里定義）

考慮到fb_ops結構體里面的函數指針成員太多，這里僅簡單列舉幾個比較常見的，具體的請參考源代碼。

struct fb_ops{
struct module *owner; /* 模塊計數 */
int (*fb_open)(struct fb_info *info, int user); /* 打開函數，第一個參數為fb_info */
int (*fb_release)(struct fb_info *info, int user);
。。。。。。
/* fb_check_var函數用來檢查可變參數，並調整修改可變參數 */
int (*fb_check_var)(struct fb_var_screeninfo *var, struct fb_info *info);
。。。。。。
/*fb_setcolreg函數就是用來設置fb_info里面的pseudo_palette調色板成員 */
int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green,
unsigned blue, unsigned transp, struct fb_info *info);
。。。。。。

/* 下面三個是通用的函數 */
/* Draws a rectangle */
void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);
/* Copy data from area to another */
void (*fb_copyarea) (struct fb_info *info, const struct fb_copyarea *region);
/* Draws a image to the display */
void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);
。。。。。。
/* 有了fb_ioctl應用層可以通過ioctl系統調用來設置屏幕參數等 */
int (*fb_ioctl)(struct fb_info *info, unsigned int cmd,
unsigned long arg);
。。。。。。
/* 有了fb_mmap應用層可以通過mmap系統調用來讀寫幀緩沖區內存 */
int (*fb_mmap)(struct fb_info *info, struct vm_area_struct *vma);
。。。
};

a：內核中數據結構

fb_var_screeninfo 結構體（在include/linux/fb.h文件里定義）

fb_var_screeninfo 被fb_info結構體所包含，這個結構體主要用來設置LCD屏幕的參數，如分辨率、像素比特數等，LCD驅動程序里面硬件相關的設置很多都涉及這個結構體。

struct fb_var_screeninfo {
__u32 xres;/* visible resolution,分辨率，即一行有多少個點 */
__u32 yres;
__u32 xres_virtual;/* virtual resolution*/
__u32 yres_virtual;
__u32 xoffset;/* offset from virtual to visible */
__u32 yoffset;/* resolution*/

__u32 bits_per_pixel;/* guess what，定義每個點用多少個自己表示 */
__u32 grayscale;/* != 0 Graylevels instead of colors */

struct fb_bitfield red;/* bitfield in fb mem if true color, */
struct fb_bitfield green;/* else only length is significant */
struct fb_bitfield blue;
struct fb_bitfield transp;/* transparency*/

__u32 nonstd; /* != 0 Non standard pixel format */

__u32 activate;/* see FB_ACTIVATE_**/

__u32 height;/* height of picture in mm */
__u32 width;/* width of picture in mm */

__u32 accel_flags;/* (OBSOLETE) see fb_info.flags */

/* Timing: All values in pixclocks, except pixclock (of course) */
__u32 pixclock;/* pixel clock in ps (pico seconds) */
__u32 left_margin;/* time from sync to picture*/
__u32 right_margin;/* time from picture to sync*/
__u32 upper_margin;/* time from sync to picture*/
__u32 lower_margin;
__u32 hsync_len;/* length of horizontal sync*/
__u32 vsync_len;/* length of vertical sync*/
__u32 sync; /* see FB_SYNC_**/
__u32 vmode; /* see FB_VMODE_**/
__u32 rotate; /* angle we rotate counter clockwise */
__u32 reserved[5];/* Reserved for future compatibility */
};

a:內核數據結構

fb_fix_screeninfo 結構體（在include/linux/fb.h文件里定義）

struct fb_fix_screeninfo {
char id[16];/* 驅動名字就保存在這里*/
unsigned long smem_start; /* fb緩沖區的基地址，這是一個物理地址 */
__u32 smem_len; /* fb緩沖區的長度 */
__u32 type; /* FB_TYPE_類型*/
__u32 type_aux;/* Interleave for interleaved Planes */
__u32 visual;/* FB_VISUAL_類型*/
__u16 xpanstep;/* 一般設置為0 */
__u16 ypanstep;/* 一般設置為0 */
__u16 ywrapstep;/* 一般設置為0 */
__u32 line_length;/* 屏幕一行有多個字節 */
unsigned long mmio_start;/* Start of Memory Mapped I/O */
/* (physical address) */
__u32 mmio_len;/* Length of Memory Mapped I/O */
__u32 accel; /* Indicate to driver which*/
/* specific chip/card we have*/
__u16 reserved[3];/* Reserved for future compatibility */
};

<LCD驅動實例一>

我們的mini2440使用的是X35的LCD屏，根據X35的LCD說明文檔，需要在BSP中X35LCD屏的一些參數。

在mach-mini2440.c中添加X35LCD的參數

#if defined(CONFIG_FB_S3C2410_X240320) //定義X35LCD參數

#define LCD_WIDTH 240 //屏寬

#define LCD_HEIGHT 320 //屏高

#define LCD_PIXCLOCK 170000 //時鍾

#define LCD_RIGHT_MARGIN 25 //左邊界

#define LCD_LEFT_MARGIN 0 //右邊界

#define LCD_HSYNC_LEN 4 //行同步

#define LCD_UPPER_MARGIN 0 //上邊界

#define LCD_LOWER_MARGIN 4 //下邊界

#define LCD_VSYNC_LEN 9 //幀同步

#elif //定義其他LCD屏參數

#endif

好了，我們現在發現要想上面定義的X35LCD的參數正在起作用，必須使得CONFIG_FB_S3C2410_X240320=y；我們需要在/driver/video/Kconfig中定義

config FB_S3C2410_X240320

boolean "3.5 inch 240X320 LCD(ACX502BMU)"

depends on FB_S3C2410

help

3.5 inch 240X320 LCD(ACX502BMU)

然后我們通過make menuconfig選中"3.5 inch 240X320 LCD(ACX502BMU)"這一選項。

根據我們的X35LCD屏的說明文檔，我們已經定義了一些邊界參數和同步參數，因為我們的LCD驅動是基於platform總線的，所以需要在這個BSP中添加LCD的平台設備。

struct platform_device s3c_device_lcd = { //添加LCD平台設備

.name = "s3c2410-lcd", //設備名

.id = -1,

.num_resources = ARRAY_SIZE(s3c_lcd_resource),

.resource = s3c_lcd_resource, //資源

.dev = {

.dma_mask = &s3c_device_lcd_dmamask,

.coherent_dma_mask = 0xffffffffUL

}

};

資源的定義如下

static struct resource s3c_lcd_resource[] = {

[0] = { //內存空間資源

.start = S3C24XX_PA_LCD,

.end = S3C24XX_PA_LCD + S3C24XX_SZ_LCD - 1,

.flags = IORESOURCE_MEM,

[1] = { //中斷資源

.start = IRQ_LCD,

.end = IRQ_LCD,

.flags = IORESOURCE_IRQ,

}

};

然后我們把s3c_device_lcd放到mini2440_devices[]結構體中，接着調用platform_add_devices(mini2440_devices, ARRAY_SIZE(mini2440_devices))將LCD平台設備注冊到內核。

對於我們的LCD，需要給這個平台設備添加平台設備數據，通過調用

s3c24xx_fb_set_platdata(&mini2440_fb_info);

static struct s3c2410fb_mach_info mini2440_fb_info __initdata = {

.displays = &mini2440_lcd_cfg, //定義s3c2410fb_display數據

.num_displays = 1,

.default_display = 0,

.gpccon = 0xaa955699, //GPC端口設置

.gpccon_mask = 0xffc003cc,

.gpcup = 0x0000ffff,

.gpcup_mask = 0xffffffff,

.gpdcon = 0xaa95aaa1, //GPD端口設置

.gpdcon_mask = 0xffc0fff0,

.gpdup = 0x0000faff,

.gpdup_mask = 0xffffffff,

.lpcsel = 0xf82,

};

繼續看

static struct s3c2410fb_display mini2440_lcd_cfg __initdata = {

#if !defined (LCD_CON5)

.lcdcon5 = S3C2410_LCDCON5_FRM565 |

S3C2410_LCDCON5_INVVLINE |

S3C2410_LCDCON5_INVVFRAME |

S3C2410_LCDCON5_PWREN |

S3C2410_LCDCON5_HWSWP,

#else

.lcdcon5 = LCD_CON5,

#endif

.type = S3C2410_LCDCON1_TFT, //屏的類型

.width = LCD_WIDTH, //屏寬

.height = LCD_HEIGHT, //屏高

.pixclock = LCD_PIXCLOCK, //時鍾

.xres = LCD_WIDTH, //水平分辨率

.yres = LCD_HEIGHT, //垂直分辨率

.bpp = 16, //每個像素的比特數

.left_margin = LCD_LEFT_MARGIN + 1, //左邊界

.right_margin = LCD_RIGHT_MARGIN + 1, //右邊界

.hsync_len = LCD_HSYNC_LEN + 1, //行同步

.upper_margin = LCD_UPPER_MARGIN + 1, //上邊界

.lower_margin = LCD_LOWER_MARGIN + 1, //下邊界

.vsync_len = LCD_VSYNC_LEN + 1, //幀同步

};

好了，這樣我們就完成了LCD驅動的移植工作，接着我們通過make menuconfig選擇相應的文件層、設備層和X35LCD屏這個三個選項，最后編譯生成內核。

三．LCD文件層和驅動層設計思路

LCD驅動可以分為文件層和設備層，文件層又叫FrameBuffer設備驅動，對應的文件是fbmem.c，主要實現為用戶提供file_operations接口，同時為設備層提供一些函數接口，這個幀緩沖設備驅動內核已經幫我們編寫好，我們不需要編寫。在設備層我們專門Mini2440的LCD編寫的驅動在s3c2410fb.c中，該驅動叫LCD驅動，主要是填充一個fbinfo結構，然后用register_framebuffer注冊到內核，對於fbinfo結構，最主要的是填充它的fs_ops成員。對於驅動工程師，第一件事就是學會根據LCD說明文檔，移植LCD。第二件事就是會寫設備層LCD驅動。

3.1 LCD驅動中幾個重要的數據結構

在分析內核LCD驅動代碼之前，我們先要熟悉幾個結構體。

struct fb_info {

int node;

int flags;

struct mutex lock;

struct mutex mm_lock;

struct fb_var_screeninfo var; //當前緩沖區的可變參數

struct fb_fix_screeninfo fix; //當前緩沖區的固定參數

struct fb_monspecs monspecs;

struct work_struct queue;

struct fb_pixmap pixmap;

struct fb_pixmap sprite;

struct fb_cmap cmap; //當前的調試板

struct list_head modelist;

struct fb_videomode *mode;

#ifdef CONFIG_FB_BACKLIGHT //背光

struct backlight_device *bl_dev;

struct mutex bl_curve_mutex; //背光燈層次

u8 bl_curve[FB_BACKLIGHT_LEVELS]; //調整背光燈

#endif

#ifdef CONFIG_FB_DEFERRED_IO

struct delayed_work deferred_work;

struct fb_deferred_io *fbdefio;

#endif

struct fb_ops *fbops; //幀緩沖操作函數集合

struct device *device;

struct device *dev;

int class_flag;

#ifdef CONFIG_FB_TILEBLITTING

struct fb_tile_ops *tileops;

#endif

char __iomem *screen_base; //虛擬基地址

unsigned long screen_size; //虛擬內存大小

void *pseudo_palette;

#define FBINFO_STATE_RUNNING 0

#define FBINFO_STATE_SUSPENDED 1

u32 state;

void *fbcon_par;

void *par; //私有數據

resource_size_t aperture_base;

resource_size_t aperture_size;

};

為了清晰起見，對於fb_info結構體，我只注釋了重點幾個成員，每個幀設備都有一個fb_info，該結構體包含了驅動實現的底層函數和記錄設備狀態的數據。fb_info結構體主要包含fb_var_screeninfo、fb_fix_screeninfo、fb_cmap和fb_ops，

struct fb_var_screeninfo {

__u32 xres; //水平分辨率

__u32 yres; //垂直分辨率

__u32 xres_virtual;

__u32 yres_virtual;

__u32 xoffset;

__u32 yoffset;

__u32 bits_per_pixel; //每個像素所占的比特數

__u32 grayscale;

struct fb_bitfield red;

struct fb_bitfield green;

struct fb_bitfield blue;

struct fb_bitfield transp;

__u32 nonstd;

__u32 activate;

__u32 height; //屏高

__u32 width; //屏寬

__u32 accel_flags;

__u32 pixclock; //像素時鍾

__u32 left_margin; //左邊界

__u32 right_margin; //右邊界

__u32 upper_margin; //上邊界

__u32 lower_margin; //下邊界

__u32 hsync_len; //水平同步長度

__u32 vsync_len; //垂直同步長度

__u32 sync;

__u32 vmode;

__u32 rotate;

__u32 reserved[5];

};

上面的fb_var_screeninfo結構體存放了用戶可以修改的顯示控制器參數，如分辨率，BPP等參數。

struct fb_fix_screeninfo {

char id[16];

unsigned long smem_start; //fb緩沖區開始的位置

__u32 smem_len; //fb緩沖區長度

__u32 type;

__u32 type_aux;

__u32 visual; //屏幕色彩模式

__u16 xpanstep;

__u16 ypanstep;

__u16 ywrapstep;

__u32 line_length;

unsigned long mmio_start; //內存映射開始位置

__u32 mmio_len; //內存映射長度

__u32 accel;

__u16 reserved[3];

};

上面這個fb_fix_screeninfo主要記錄了用戶不能修改的固定顯示控制器參數，如緩沖區物理地址、緩沖區長度、顯示色彩模式、內核映射的開始位置等，這些結構體程序都需要驅動程序初始化時設置。

struct fb_cmap {

__u32 start; //顏色板的第一個元素入口位置

__u32 len; //元素長度

__u16 *red; //紅

__u16 *green; //綠

__u16 *blue; //藍

__u16 *transp; //透明分量值

};

對於上面的fb_cmap，它主要記錄了一個顏色板信息，用戶空間可以使用ioctl函數的FBIOGETCMAP和FBIOPUTCMAP讀取和設置顏色表的值。

struct fb_ops {

struct module *owner;

int (*fb_open)(struct fb_info *info, int user);

int (*fb_release)(struct fb_info *info, int user);

ssize_t (*fb_read)(struct fb_info *info, char __user *buf,

size_t count, loff_t *ppos);

ssize_t (*fb_write)(struct fb_info *info, const char __user *buf,

size_t count, loff_t *ppos);

int (*fb_check_var)(struct fb_var_screeninfo *var, struct fb_info *info);

int (*fb_set_par)(struct fb_info *info);

int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green,

unsigned blue, unsigned transp, struct fb_info *info);

int (*fb_setcmap)(struct fb_cmap *cmap, struct fb_info *info);

int (*fb_blank)(int blank, struct fb_info *info);

int (*fb_pan_display)(struct fb_var_screeninfo *var, struct fb_info *info);

void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);

void (*fb_copyarea) (struct fb_info *info, const struct fb_copyarea *region);

void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);

int (*fb_cursor) (struct fb_info *info, struct fb_cursor *cursor);

void (*fb_rotate)(struct fb_info *info, int angle);

int (*fb_sync)(struct fb_info *info);

int (*fb_ioctl)(struct fb_info *info, unsigned int cmd,

unsigned long arg);

int (*fb_compat_ioctl)(struct fb_info *info, unsigned cmd,

unsigned long arg);

int (*fb_mmap)(struct fb_info *info, struct vm_area_struct *vma);

void (*fb_get_caps)(struct fb_info *info, struct fb_blit_caps *caps,

struct fb_var_screeninfo *var);

void (*fb_destroy)(struct fb_info *info);

};

其中fb_ops就是用來實現對幀緩沖設備的操作。

3.2 LCD驅動層

好了，我們先看看驅動層代碼s3c2410fb.c

static struct platform_driver s3c2410fb_driver = {

.probe = s3c2410fb_probe, //探測

.remove = s3c2410fb_remove, //移除

.suspend = s3c2410fb_suspend, //掛起

.resume = s3c2410fb_resume, //恢復

.driver = {

.name = "s3c2410-lcd", //驅動名

.owner = THIS_MODULE,

};

我們看看探測函數s3c2410fb_probe

static int __init s3c2410fb_probe(struct platform_device *pdev)

{

return s3c24xxfb_probe(pdev, DRV_S3C2410);

}

繼續看

static int __init s3c24xxfb_probe(struct platform_device *pdev,

enum s3c_drv_type drv_type)

{

struct s3c2410fb_info *info; //該驅動的全局變量結構體

struct s3c2410fb_display *display; //LCD屏的配置信息

struct fb_info *fbinfo; //幀緩沖驅動中對應的fb_info結構體

struct s3c2410fb_mach_info *mach_info; //內核平台設備數據

struct resource *res; //LCD資源

int ret;

int irq;

int i;

int size;

u32 lcdcon1;

mach_info = pdev->dev.platform_data; //獲得平台設備數據

if (mach_info == NULL) {

dev_err(&pdev->dev,

"no platform data for lcd, cannot attach\n");

return -EINVAL;

}

if (mach_info->default_display >= mach_info->num_displays) {

dev_err(&pdev->dev, "default is %d but only %d displays\n",

mach_info->default_display, mach_info->num_displays);

return -EINVAL;

}

//獲得LCD配置信息結構體

display = mach_info->displays + mach_info->default_display;

irq = platform_get_irq(pdev, 0); //獲得中斷號

if (irq < 0) {

dev_err(&pdev->dev, "no irq for device\n");

return -ENOENT;

}

//給幀緩沖fb_info分配空間，並將struct s3c2410fb_info作為其私有數據

fbinfo = framebuffer_alloc(sizeof(struct s3c2410fb_info), &pdev->dev);

if (!fbinfo)

return -ENOMEM;

platform_set_drvdata(pdev, fbinfo); //把fb_info作為平台設備的私有數據

info = fbinfo->par; //獲得fb_info的私有數據

info->dev = &pdev->dev;

info->drv_type = drv_type;

res = platform_get_resource(pdev, IORESOURCE_MEM, 0);//獲取資源

if (res == NULL) {

dev_err(&pdev->dev, "failed to get memory registers\n");

ret = -ENXIO;

goto dealloc_fb;

}

size = (res->end - res->start) + 1;

info->mem = request_mem_region(res->start, size, pdev->name); //申請內存

if (info->mem == NULL) {

dev_err(&pdev->dev, "failed to get memory region\n");

ret = -ENOENT;

goto dealloc_fb;

}

info->io = ioremap(res->start, size); //物理地址轉換為虛擬地址

if (info->io == NULL) {

dev_err(&pdev->dev, "ioremap() of registers failed\n");

ret = -ENXIO;

goto release_mem;

}

info->irq_base = info->io + ((drv_type == DRV_S3C2412) ? S3C2412_LCDINTBASE : S3C2410_LCDINTBASE); //基地址

dprintk("devinit\n");

strcpy(fbinfo->fix.id, driver_name); //驅動名

lcdcon1 = readl(info->io + S3C2410_LCDCON1);

writel(lcdcon1 & ~S3C2410_LCDCON1_ENVID, info->io + S3C2410_LCDCON1); //禁止輸出使能

fbinfo->fix.type = FB_TYPE_PACKED_PIXELS;

fbinfo->fix.type_aux = 0; //LCD屏固定參數設置

fbinfo->fix.xpanstep = 0;

fbinfo->fix.ypanstep = 0;

fbinfo->fix.ywrapstep = 0;

fbinfo->fix.accel = FB_ACCEL_NONE;

fbinfo->var.nonstd = 0; //LCD屏可變參數設置

fbinfo->var.activate = FB_ACTIVATE_NOW;

fbinfo->var.accel_flags = 0;

fbinfo->var.vmode = FB_VMODE_NONINTERLACED;

fbinfo->fbops = &s3c2410fb_ops; //操作函數集合

fbinfo->flags = FBINFO_FLAG_DEFAULT;

fbinfo->pseudo_palette = &info->pseudo_pal;

for (i = 0; i < 256; i++)

info->palette_buffer[i] = PALETTE_BUFF_CLEAR;//初始化調試板為空

ret = request_irq(irq, s3c2410fb_irq, IRQF_DISABLED, pdev->name, info);

if (ret) {

dev_err(&pdev->dev, "cannot get irq %d - err %d\n", irq, ret);

ret = -EBUSY;

goto release_regs;

}

info->clk = clk_get(NULL, "lcd"); //獲取時鍾

if (!info->clk || IS_ERR(info->clk)) {

printk(KERN_ERR "failed to get lcd clock source\n");

ret = -ENOENT;

goto release_irq;

}

clk_enable(info->clk); //使能時鍾

dprintk("got and enabled clock\n");

msleep(1);

info->clk_rate = clk_get_rate(info->clk) //設置時鍾;

for (i = 0; i < mach_info->num_displays; i++) { //獲取最大需要的顯存大小

unsigned long smem_len = mach_info->displays[i].xres;

smem_len *= mach_info->displays[i].yres;

smem_len *= mach_info->displays[i].bpp;

smem_len >>= 3;

if (fbinfo->fix.smem_len < smem_len)

fbinfo->fix.smem_len = smem_len;

}

//申請fb_info的顯示緩沖區空間，並將其地址寫入fbinfo中

ret = s3c2410fb_map_video_memory(fbinfo);

if (ret) {

printk(KERN_ERR "Failed to allocate video RAM: %d\n", ret);

ret = -ENOMEM;

goto release_clock;

}

dprintk("got video memory\n");

fbinfo->var.xres = display->xres; //水平分辨率

fbinfo->var.yres = display->yres; //垂直分辨率

fbinfo->var.bits_per_pixel = display->bpp; //每個像素的比特數

s3c2410fb_init_registers(fbinfo); //初始化GPIO寄存器

//檢查fb_info->var與fbinfo支持的哪一種分辨率、色彩模式匹配

s3c2410fb_check_var(&fbinfo->var, fbinfo);

ret = s3c2410fb_cpufreq_register(info);

if (ret < 0) {

dev_err(&pdev->dev, "Failed to register cpufreq\n");

goto free_video_memory;

}

ret = register_framebuffer(fbinfo);//注冊幀緩沖設備fb_info到系統中

if (ret < 0) {

printk(KERN_ERR "Failed to register framebuffer device: %d\n",

ret);

goto free_cpufreq;

}

ret = device_create_file(&pdev->dev, &dev_attr_debug);

if (ret) {

printk(KERN_ERR "failed to add debug attribute\n");

}

printk(KERN_INFO "fb%d: %s frame buffer device\n",

fbinfo->node, fbinfo->fix.id);

return 0;

free_cpufreq:

s3c2410fb_cpufreq_deregister(info);

free_video_memory:

s3c2410fb_unmap_video_memory(fbinfo);

release_clock:

clk_disable(info->clk);

clk_put(info->clk);

release_irq:

free_irq(irq, info);

release_regs:

iounmap(info->io);

release_mem:

release_resource(info->mem);

kfree(info->mem);

dealloc_fb:

platform_set_drvdata(pdev, NULL);

framebuffer_release(fbinfo);

return ret;

}

上面這個探測函數中包含了幾個重要的函數，如申請幀緩沖設備的顯存區空間的函數s3c2410fb_map_video_memory(fbinfo)；初始化GPIO寄存器的函數s3c2410fb_init_registers(fbinfo)；檢查fb_info->var與fbinfo支持的哪一種分辨率、色彩模式匹配，並據此填充var中其他參數的函數s3c2410fb_check_var(&fbinfo->var, fbinfo)，下面我們依次對這三個函數進行分析。

首先看s3c2410fb_map_video_memory(fbinfo)，即申請幀緩沖設備的顯存區空間的函數

static int __init s3c2410fb_map_video_memory(struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par; //獲得fb_info的私有數據

dma_addr_t map_dma; //保存DMA緩沖區總線地址

unsigned map_size = PAGE_ALIGN(info->fix.smem_len);

dprintk("map_video_memory(fbi=%p) map_size %u\n", fbi, map_size);

//將分配的一個寫合並DMA緩存區設置為LCD屏幕的虛擬地址

info->screen_base = dma_alloc_writecombine(fbi->dev, map_size,

&map_dma, GFP_KERNEL);

if (info->screen_base) {

dprintk("map_video_memory: clear %p:%08x\n",

info->screen_base, map_size);

memset(info->screen_base, 0x00, map_size); //設置DMA緩存內容為空

//將DMA緩沖區總線地址設為fb_info不可變參數中緩存的開始位置

info->fix.smem_start = map_dma;

dprintk("map_video_memory: dma=%08lx cpu=%p size=%08x\n",

info->fix.smem_start, info->screen_base, map_size);

}

return info->screen_base ? 0 : -ENOMEM;

}

接着我們看看初始化GPIO寄存器的函數s3c2410fb_init_registers(fbinfo)

static int s3c2410fb_init_registers(struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par; //獲得fb_info的私有數據

struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;

unsigned long flags;

void __iomem *regs = fbi->io;

void __iomem *tpal;

void __iomem *lpcsel;

if (is_s3c2412(fbi)) {

tpal = regs + S3C2412_TPAL;

lpcsel = regs + S3C2412_TCONSEL;

} else {

tpal = regs + S3C2410_TPAL;

lpcsel = regs + S3C2410_LPCSEL;

}

local_irq_save(flags);

//把GPIO端口C和D配置成LCD模式

modify_gpio(S3C2410_GPCUP, mach_info->gpcup, mach_info->gpcup_mask);

modify_gpio(S3C2410_GPCCON, mach_info->gpccon, mach_info->gpccon_mask);

modify_gpio(S3C2410_GPDUP, mach_info->gpdup, mach_info->gpdup_mask);

modify_gpio(S3C2410_GPDCON, mach_info->gpdcon, mach_info->gpdcon_mask);

local_irq_restore(flags);

dprintk("LPCSEL = 0x%08lx\n", mach_info->lpcsel);

writel(mach_info->lpcsel, lpcsel);

dprintk("replacing TPAL %08x\n", readl(tpal));

writel(0x00, tpal);

return 0;

}

最后看看檢查fb_info->var與fbinfo支持的哪一種分辨率、色彩模式匹配，並據此填充var中其他參數的函數s3c2410fb_check_var(&fbinfo->var, fbinfo)

static int s3c2410fb_check_var(struct fb_var_screeninfo *var,

struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par;

struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;

struct s3c2410fb_display *display = NULL;

struct s3c2410fb_display *default_display = mach_info->displays +

mach_info->default_display;

int type = default_display->type; //獲取LCD類型，TFT

unsigned i;

dprintk("check_var(var=%p, info=%p)\n", var, info);

//驗證x/y解析度

if (var->yres == default_display->yres &&

var->xres == default_display->xres &&

var->bits_per_pixel == default_display->bpp)

display = default_display;

else

for (i = 0; i < mach_info->num_displays; i++)

if (type == mach_info->displays[i].type &&

var->yres == mach_info->displays[i].yres &&

var->xres == mach_info->displays[i].xres &&

var->bits_per_pixel == mach_info->displays[i].bpp) {

display = mach_info->displays + i;

break;

}

if (!display) {

dprintk("wrong resolution or depth %dx%d at %d bpp\n",

var->xres, var->yres, var->bits_per_pixel);

return -EINVAL;

}

var->xres_virtual = display->xres; //配置屏的虛擬解析像素

var->yres_virtual = display->yres;

var->height = display->height; //配置屏的高度寬度

var->width = display->width;

var->pixclock = display->pixclock; //配置屏的時鍾

var->left_margin = display->left_margin; //配置屏的行幀同步、水平垂直同步

var->right_margin = display->right_margin;

var->upper_margin = display->upper_margin;

var->lower_margin = display->lower_margin;

var->vsync_len = display->vsync_len;

var->hsync_len = display->hsync_len;

fbi->regs.lcdcon5 = display->lcdcon5; ///配置LCD寄存器

fbi->regs.lcdcon1 = display->type;

var->transp.offset = 0; //配置透明度

var->transp.length = 0;

//根據BBP來設置可變參數RGB的顏色位域

switch (var->bits_per_pixel) {

case 1:

case 2:

case 4:

var->red.offset = 0;

var->red.length = var->bits_per_pixel;

var->green = var->red;

var->blue = var->red;

break;

case 8:

if (display->type != S3C2410_LCDCON1_TFT) {

var->red.length = 3;

var->red.offset = 5;

var->green.length = 3;

var->green.offset = 2;

var->blue.length = 2;

var->blue.offset = 0;

} else {

var->red.offset = 0;

var->red.length = 8;

var->green = var->red;

var->blue = var->red;

}

break;

case 12:

var->red.length = 4;

var->red.offset = 8;

var->green.length = 4;

var->green.offset = 4;

var->blue.length = 4;

var->blue.offset = 0;

break;

default:

case 16:

if (display->lcdcon5 & S3C2410_LCDCON5_FRM565) {

var->red.offset = 11; //偏移

var->green.offset = 5;

var->blue.offset = 0;

var->red.length = 5; //長度

var->green.length = 6;

var->blue.length = 5;

} else {

var->red.offset = 11;

var->green.offset = 6;

var->blue.offset = 1;

var->red.length = 5;

var->green.length = 5;

var->blue.length = 5;

}

break;

case 32:

var->red.length = 8;

var->red.offset = 16;

var->green.length = 8;

var->green.offset = 8;

var->blue.length = 8;

var->blue.offset = 0;

break;

}

return 0;

}

好了，我們已經分析完LCD驅動中probe探測函數了，該函數主要是分配fb_info結構體空間，然后填充fb_info，初始化GPIO控制器，檢查並設置fb_info中可變參數，申請幀緩沖設備的顯示緩沖區空間，最后調用register_framebuffer函數注冊到內核。

下面我們把重點放在fb_info結構體的fb_ops成員上

static struct fb_ops s3c2410fb_ops = {

.owner = THIS_MODULE,

.fb_check_var = s3c2410fb_check_var, //檢查參數

.fb_set_par = s3c2410fb_set_par, //激活fb_info參數配置

.fb_blank = s3c2410fb_blank, //顯示空白

.fb_setcolreg = s3c2410fb_setcolreg, //設置顏色表

.fb_fillrect = cfb_fillrect, //可選

.fb_copyarea = cfb_copyarea, //可選

.fb_imageblit = cfb_imageblit, //可選

};

fp_ops是使得幀緩沖設備工作所需函數的集合，它們最終與LCD控制器打交道。

s3c2410fb_check_va用於調整可變參數，並修改為硬件所支持的值；s3c2410fb_set_par則根據屏幕參數設置具體讀寫LCD控制器的寄存器，使得LCD控制器進入相應的工作狀態。對於fb_ops中的.fb_fillrect、fb_copyarea和fb_imageblit，我們通常使用通用的cfb_fillrect、cfb_copyarea和cfb_imageblit函數即可。s3c2410fb_setcolreg是用來實現偽顏色表和顏色表的填充。

對於fb_ops中的成員中s3c2410fb_check_va這個函數在上面probe探測函數中已經講過了，剩下的任務就是分析下激活fb_info參數配置函數s3c2410fb_set_par和顯示空白函數s3c2410fb_blank。

首先看看顯示空白函數s3c2410fb_blank

static int s3c2410fb_blank(int blank_mode, struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par; //獲得fb_info私有數據

void __iomem *tpal_reg = fbi->io; //獲得內存指針

dprintk("blank(mode=%d, info=%p)\n", blank_mode, info);

tpal_reg += is_s3c2412(fbi) ? S3C2412_TPAL : S3C2410_TPAL;

//根據顯示空白的模式設置LCD開啟或停止

if (blank_mode == FB_BLANK_POWERDOWN) {

s3c2410fb_lcd_enable(fbi, 0); //停止LCD

} else {

s3c2410fb_lcd_enable(fbi, 1); //開啟LCD

}

//根據顯示空白的模式控制臨時調色板是否有效

if (blank_mode == FB_BLANK_UNBLANK)

writel(0x0, tpal_reg); //調色板寄存器無效

else {

dprintk("setting TPAL to output 0x000000\n");

writel(S3C2410_TPAL_EN, tpal_reg); //調色板寄存器有效

}

return 0;

}

跟蹤s3c2410fb_blank中的s3c2410fb_lcd_enable函數

static void s3c2410fb_lcd_enable(struct s3c2410fb_info *fbi, int enable)

{

unsigned long flags;

local_irq_save(flags);

if (enable)

fbi->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID; //開啟LCD

else

fbi->regs.lcdcon1 &= ~S3C2410_LCDCON1_ENVID; //關閉LCD

writel(fbi->regs.lcdcon1, fbi->io + S3C2410_LCDCON1);

local_irq_restore(flags);

}

接着看看這個根據fbinfo->var激活fb_info中的參數配置函數s3c2410fb_set_par

static int s3c2410fb_set_par(struct fb_info *info)

{

struct fb_var_screeninfo *var = &info->var;

switch (var->bits_per_pixel) {//根據色位模式設置色彩模式

case 32:

case 16:

case 12:

info->fix.visual = FB_VISUAL_TRUECOLOR;

break;

case 1:

info->fix.visual = FB_VISUAL_MONO01;

break;

default:

info->fix.visual = FB_VISUAL_PSEUDOCOLOR;

break;

}

//設置fb_info中固定參數中一行的字節數

info->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8;

s3c2410fb_activate_var(info); //激活fb_info參數配置

return 0;

}

我們看看s3c2410fb_set_par中激活fb_info參數配置函數s3c2410fb_activate_var

static void s3c2410fb_activate_var(struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par;

void __iomem *regs = fbi->io;

int type = fbi->regs.lcdcon1 & S3C2410_LCDCON1_TFT;

struct fb_var_screeninfo *var = &info->var;

int clkdiv;

//計算LCD控制器1中的CLKVAL值

clkdiv = DIV_ROUND_UP(s3c2410fb_calc_pixclk(fbi, var->pixclock), 2);

dprintk("%s: var->xres = %d\n", __func__, var->xres);

dprintk("%s: var->yres = %d\n", __func__, var->yres);

dprintk("%s: var->bpp = %d\n", __func__, var->bits_per_pixel);

if (type == S3C2410_LCDCON1_TFT) { //配置TFT屏LCD控制寄存器

s3c2410fb_calculate_tft_lcd_regs(info, &fbi->regs);

--clkdiv;

if (clkdiv < 0)

clkdiv = 0;

} else { //配置STN屏LCD控制寄存器

s3c2410fb_calculate_stn_lcd_regs(info, &fbi->regs);

if (clkdiv < 2)

clkdiv = 2;

}

//設置LCD控制器1中的CLKVAL值

fbi->regs.lcdcon1 |= S3C2410_LCDCON1_CLKVAL(clkdiv);

dprintk("new register set:\n");

dprintk("lcdcon[1] = 0x%08lx\n", fbi->regs.lcdcon1);

dprintk("lcdcon[2] = 0x%08lx\n", fbi->regs.lcdcon2);

dprintk("lcdcon[3] = 0x%08lx\n", fbi->regs.lcdcon3);

dprintk("lcdcon[4] = 0x%08lx\n", fbi->regs.lcdcon4);

dprintk("lcdcon[5] = 0x%08lx\n", fbi->regs.lcdcon5);

//設置LCD控制器1-5的參數

writel(fbi->regs.lcdcon1 & ~S3C2410_LCDCON1_ENVID,

regs + S3C2410_LCDCON1);

writel(fbi->regs.lcdcon2, regs + S3C2410_LCDCON2);

writel(fbi->regs.lcdcon3, regs + S3C2410_LCDCON3);

writel(fbi->regs.lcdcon4, regs + S3C2410_LCDCON4);

writel(fbi->regs.lcdcon5, regs + S3C2410_LCDCON5);

s3c2410fb_set_lcdaddr(info); //設置幀緩沖起始地址寄存器1-3

fbi->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID,

writel(fbi->regs.lcdcon1, regs + S3C2410_LCDCON1);

}

下面我們主要關注s3c2410fb_calculate_tft_lcd_regs和s3c2410fb_set_lcdaddr函數

static void s3c2410fb_calculate_tft_lcd_regs(const struct fb_info *info,

struct s3c2410fb_hw *regs)

{

const struct s3c2410fb_info *fbi = info->par;

const struct fb_var_screeninfo *var = &info->var;

switch (var->bits_per_pixel) {//根據色模式設置LCD控制器1和5

case 1:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT1BPP;

break;

case 2:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT2BPP;

break;

case 4:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT4BPP;

break;

case 8:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT8BPP;

regs->lcdcon5 |= S3C2410_LCDCON5_BSWP |

S3C2410_LCDCON5_FRM565;

regs->lcdcon5 &= ~S3C2410_LCDCON5_HWSWP;

break;

case 16:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT16BPP;

regs->lcdcon5 &= ~S3C2410_LCDCON5_BSWP;

regs->lcdcon5 |= S3C2410_LCDCON5_HWSWP;

break;

case 32:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT24BPP;

regs->lcdcon5 &= ~(S3C2410_LCDCON5_BSWP |

S3C2410_LCDCON5_HWSWP |

S3C2410_LCDCON5_BPP24BL);

break;

default:

dev_err(fbi->dev, "invalid bpp %d\n",

var->bits_per_pixel);

}

dprintk("setting vert: up=%d, low=%d, sync=%d\n",

var->upper_margin, var->lower_margin, var->vsync_len);

dprintk("setting horz: lft=%d, rt=%d, sync=%d\n",

var->left_margin, var->right_margin, var->hsync_len);

//設置LCD控制器2、3、4

regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1) |

S3C2410_LCDCON2_VBPD(var->upper_margin - 1) |

S3C2410_LCDCON2_VFPD(var->lower_margin - 1) |

S3C2410_LCDCON2_VSPW(var->vsync_len - 1);

regs->lcdcon3 = S3C2410_LCDCON3_HBPD(var->right_margin - 1) |

S3C2410_LCDCON3_HFPD(var->left_margin - 1) |

S3C2410_LCDCON3_HOZVAL(var->xres - 1);

regs->lcdcon4 = S3C2410_LCDCON4_HSPW(var->hsync_len - 1);

}

static void s3c2410fb_set_lcdaddr(struct fb_info *info)

{

unsigned long saddr1, saddr2, saddr3;

struct s3c2410fb_info *fbi = info->par;

void __iomem *regs = fbi->io;

saddr1 = info->fix.smem_start >> 1;

saddr2 = info->fix.smem_start;

saddr2 += info->fix.line_length * info->var.yres;

saddr2 >>= 1;

saddr3 = S3C2410_OFFSIZE(0) |

S3C2410_PAGEWIDTH((info->fix.line_length / 2) & 0x3ff);

dprintk("LCDSADDR1 = 0x%08lx\n", saddr1);

dprintk("LCDSADDR2 = 0x%08lx\n", saddr2);

dprintk("LCDSADDR3 = 0x%08lx\n", saddr3);

//初始化LCD控制器的地址指針

writel(saddr1, regs + S3C2410_LCDSADDR1);

writel(saddr2, regs + S3C2410_LCDSADDR2);

writel(saddr3, regs + S3C2410_LCDSADDR3);

}

歸納下我們分析的這個激活fb_info參數配置函數s3c2410fb_activate_var，該函數主要是計算clkval的值，計算LCD控制器1-5的值，然后設置LCD控制器1-5，並設置幀緩沖寄存器。

<LCD驅動實例二>

#include <linux/kernel.h> #include <linux/module.h> #include <linux/errno.h> #include <linux/init.h> #include <linux/platform_device.h> #include <linux/dma-mapping.h> #include <linux/fb.h> #include <linux/clk.h> #include <linux/interrupt.h> #include <linux/mm.h>

#include <linux/slab.h> #include <linux/delay.h> #include <asm/irq.h> #include <asm/io.h> #include <asm/div64.h> #include <mach/regs-lcd.h> #include <mach/regs-gpio.h> #include <mach/fb.h> #include <linux/pm.h>

/*FrameBuffer設備名稱*/
static char driver_name[] = "my2440_lcd";

/*定義一個結構體用來維護驅動程序中各函數中用到的變量
  先別看結構體要定義這些成員，到各函數使用的地方就明白了*/
struct my2440fb_var
{
    int lcd_irq_no;           /*保存LCD中斷號*/
    struct clk *lcd_clock;    /*保存從平台時鍾隊列中獲取的LCD時鍾*/
    struct resource *lcd_mem; /*LCD的IO空間*/
    void __iomem *lcd_base;   /*LCD的IO空間映射到虛擬地址*/
    struct device *dev;

    struct s3c2410fb_hw regs; /*表示5個LCD配置寄存器，s3c2410fb_hw定義在mach-s3c2410/include/mach/fb.h中*/

    /*定義一個數組來充當調色板。
    據數據手冊描述，TFT屏色位模式為8BPP時，調色板(顏色表)的長度為256，調色板起始地址為0x4D000400*/
    u32    palette_buffer[256];

    u32 pseudo_pal[16];
    unsigned int palette_ready; /*標識調色板是否准備好了*/
};

/*用做清空調色板(顏色表)*/
#define PALETTE_BUFF_CLEAR (0x80000000)

/*LCD平台驅動結構體，平台驅動結構體定義在platform_device.h中，該結構體成員接口函數在第②步中實現*/
static struct platform_driver lcd_fb_driver =
{
    .probe     = lcd_fb_probe,               /*FrameBuffer設備探測*/
    .remove    = __devexit_p(lcd_fb_remove), /*FrameBuffer設備移除*/
    .suspend   = lcd_fb_suspend,             /*FrameBuffer設備掛起*/
    .resume    = lcd_fb_resume,              /*FrameBuffer設備恢復*/
    .driver    =
    {
        /*注意這里的名稱一定要和系統中定義平台設備的地方一致，這樣才能把平台設備與該平台設備的驅動關聯起來*/
        .name = "s3c2410-lcd",
        .owner = THIS_MODULE,
    },
};

static int __init lcd_init(void)
{
    /*在Linux中，幀緩沖設備被看做是平台設備，所以這里注冊平台設備*/
    return platform_driver_register(&lcd_fb_driver);
}

static void __exit lcd_exit(void)
{
    /*注銷平台設備*/
    platform_driver_unregister(&lcd_fb_driver);
}

module_init(lcd_init);
module_exit(lcd_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Huang Gang");
MODULE_DESCRIPTION("My2440 LCD FrameBuffer Driver");

②、LCD平台設備各接口函數的實現：

/*LCD FrameBuffer設備探測的實現，注意這里使用一個__devinit宏，到lcd_fb_remove接口函數實現的地方講解*/ static int __devinit lcd_fb_probe(struct platform_device *pdev) { int i; int ret; struct resource *res; /*用來保存從LCD平台設備中獲取的LCD資源*/ struct fb_info *fbinfo; /*FrameBuffer驅動所對應的fb_info結構體*/ struct s3c2410fb_mach_info *mach_info; /*保存從內核中獲取的平台設備數據*/ struct my2440fb_var *fbvar; /*上面定義的驅動程序全局變量結構體*/ struct s3c2410fb_display *display; /*LCD屏的配置信息結構體，該結構體定義在mach-s3c2410/include/mach/fb.h中*/ /*獲取LCD硬件相關信息數據，在前面講過內核使用s3c24xx_fb_set_platdata函數將LCD的硬件相關信息保存到了LCD平台數據中，所以這里我們就從平台數據中取出來在驅動中使用*/ mach_info = pdev->dev.platform_data; if(mach_info == NULL) { /*判斷獲取數據是否成功*/ dev_err(&pdev->dev, "no platform data for lcd/n"); return -EINVAL; } /*獲得在內核中定義的FrameBuffer平台設備的LCD配置信息結構體數據*/ display = mach_info->displays + mach_info->default_display;

/*給fb_info分配空間，大小為my2440fb_var結構的內存，framebuffer_alloc定義在fb.h中在fbsysfs.c中實現*/ fbinfo = framebuffer_alloc(sizeof(struct my2440fb_var), &pdev->dev); if(!fbinfo) { dev_err(&pdev->dev, "framebuffer alloc of registers failed/n"); ret = -ENOMEM; goto err_noirq; } platform_set_drvdata(pdev, fbinfo);/*重新將LCD平台設備數據設置為fbinfo，好在后面的一些函數中來使用*/ /*這里的用途其實就是將fb_info的成員par(注意是一個void類型的指針)指向這里的私有變量結構體fbvar，目的是到其他接口函數中再取出fb_info的成員par，從而能繼續使用這里的私有變量*/ fbvar = fbinfo->par; fbvar->dev = &pdev->dev; /*在系統定義的LCD平台設備資源中獲取LCD中斷號,platform_get_irq定義在platform_device.h中*/ fbvar->lcd_irq_no = platform_get_irq(pdev, 0); if(fbvar->lcd_irq_no < 0) { /*判斷獲取中斷號是否成功*/ dev_err(&pdev->dev, "no lcd irq for platform/n"); return -ENOENT; } /*獲取LCD平台設備所使用的IO端口資源，注意這個IORESOURCE_MEM標志和LCD平台設備定義中的一致*/ res = platform_get_resource(pdev, IORESOURCE_MEM, 0); if(res == NULL) { /*判斷獲取資源是否成功*/ dev_err(&pdev->dev, "failed to get memory region resource/n"); return -ENOENT; } /*申請LCD IO端口所占用的IO空間(注意理解IO空間和內存空間的區別),request_mem_region定義在ioport.h中*/ fbvar->lcd_mem = request_mem_region(res->start, res->end - res->start + 1,pdev->name); if(fbvar->lcd_mem == NULL) { /*判斷申請IO空間是否成功*/ dev_err(&pdev->dev, "failed to reserve memory region/n"); return -ENOENT; } /*將LCD的IO端口占用的這段IO空間映射到內存的虛擬地址，ioremap定義在io.h中注意：IO空間要映射后才能使用，以后對虛擬地址的操作就是對IO空間的操作*/ fbvar->lcd_base = ioremap(res->start, res->end - res->start + 1); if(fbvar->lcd_base == NULL) { /*判斷映射虛擬地址是否成功*/ dev_err(&pdev->dev, "ioremap() of registers failed/n"); ret = -EINVAL; goto err_nomem; } /*從平台時鍾隊列中獲取LCD的時鍾，這里為什么要取得這個時鍾，從LCD屏的時序圖上看，各種控制信號的延遲都跟LCD的時鍾有關。系統的一些時鍾定義在arch/arm/plat-s3c24xx/s3c2410-clock.c中*/ fbvar->lcd_clock = clk_get(NULL, "lcd"); if(!fbvar->lcd_clock) { /*判斷獲取時鍾是否成功*/ dev_err(&pdev->dev, "failed to find lcd clock source/n"); ret = -ENOENT; goto err_nomap; } /*時鍾獲取后要使能后才可以使用，clk_enable定義在arch/arm/plat-s3c/clock.c中*/ clk_enable(fbvar->lcd_clock); /*申請LCD中斷服務，上面獲取的中斷號lcd_fb_irq，使用快速中斷方式:IRQF_DISABLED 中斷服務程序為:lcd_fb_irq，將LCD平台設備pdev做參數傳遞過去了*/ ret = request_irq(fbvar->lcd_irq_no, lcd_fb_irq, IRQF_DISABLED, pdev->name,fbvar); if(ret) { /*判斷申請中斷服務是否成功*/ dev_err(&pdev->dev, "IRQ%d error %d/n", fbvar->lcd_irq_no, ret); ret = -EBUSY; goto err_noclk; } /*好了，以上是對要使用的資源進行了獲取和設置。下面就開始初始化填充fb_info結構體*/ /*首先初始化fb_info中代表LCD固定參數的結構體fb_fix_screeninfo*/ /*像素值與顯示內存的映射關系有5種，定義在fb.h中。現在采用FB_TYPE_PACKED_PIXELS方式，在該方式下，像素值與內存直接對應，比如在顯示內存某單元寫入一個"1"時，該單元對應的像素值也將是"1"，這使得應用層把顯示內存映射到用戶空間變得非常方便。Linux中當LCD為TFT屏時，顯示驅動管理顯示內存就是基於這種方式*/ strcpy(fbinfo->fix.id, driver_name);/*字符串形式的標識符*/ fbinfo->fix.type = FB_TYPE_PACKED_PIXELS; fbinfo->fix.type_aux = 0;/*以下這些根據fb_fix_screeninfo定義中的描述，當沒有硬件是都設為0*/ fbinfo->fix.xpanstep = 0; fbinfo->fix.ypanstep = 0; fbinfo->fix.ywrapstep= 0; fbinfo->fix.accel = FB_ACCEL_NONE;

fbinfo

    for (i = 0; i < mach_info->num_displays; i++) /*fb緩存的長度*/
    {
        /*計算FrameBuffer緩存的最大大小，這里右移3位(即除以8)是因為色位模式BPP是以位為單位*/
        unsigned long smem_len = (mach_info->displays[i].xres * mach_info->displays[i].yres * mach_info->displays[i].bpp) >> 3;

        if(fbinfo->fix.smem_len < smem_len)
        {
            fbinfo->fix.smem_len = smem_len;
        }
    }

    /*初始化LCD控制器之前要延遲一段時間*/
    msleep(1);

    /*初始化完fb_info后，開始對LCD各寄存器進行初始化，其定義在后面講到*/
    my2440fb_init_registers(fbinfo);

    /*初始化完寄存器后，開始檢查fb_info中的可變參數，其定義在后面講到*/
    my2440fb_check_var(fbinfo);

    /*申請幀緩沖設備fb_info的顯示緩沖區空間，其定義在后面講到*/
    ret = my2440fb_map_video_memory(fbinfo);
    if (ret)
    {
        dev_err(&pdev->dev, "failed to allocate video RAM: %d/n", ret);
        ret = -ENOMEM;
        goto err_nofb;
    }

    /*最后，注冊這個幀緩沖設備fb_info到系統中, register_framebuffer定義在fb.h中在fbmem.c中實現*/
    ret = register_framebuffer(fbinfo);
    if (ret < 0)
    {
        dev_err(&pdev->dev, "failed to register framebuffer device: %d/n",ret);
        goto err_video_nomem;
    }

    /*對設備文件系統的支持(對設備文件系統的理解請參閱：嵌入式Linux之我行——設備文件系統剖析與使用)
     創建frambuffer設備文件，device_create_file定義在linux/device.h中*/
    ret = device_create_file(&pdev->dev, &dev_attr_debug);
    if (ret)
    {
        dev_err(&pdev->dev, "failed to add debug attribute/n");
    }

    return 0;

/*以下是上面錯誤處理的跳轉點*/
err_nomem:
    release_resource(fbvar->lcd_mem);
    kfree(fbvar->lcd_mem);

err_nomap:
    iounmap(fbvar->lcd_base);

err_noclk:
    clk_disable(fbvar->lcd_clock);
    clk_put(fbvar->lcd_clock);

err_noirq:
    free_irq(fbvar->lcd_irq_no, fbvar);

err_nofb:
    platform_set_drvdata(pdev, NULL);
    framebuffer_release(fbinfo);

err_video_nomem:
    my2440fb_unmap_video_memory(fbinfo);

    return ret;
}

/*LCD中斷服務程序*/
static irqreturn_t lcd_fb_irq(int irq, void *dev_id)
{
    struct my2440fb_var    *fbvar = dev_id;
    void __iomem *lcd_irq_base;
    unsigned long lcdirq;

    /*LCD中斷掛起寄存器基地址*/
    lcd_irq_base = fbvar->lcd_base + S3C2410_LCDINTBASE;

    /*讀取LCD中斷掛起寄存器的值*/
    lcdirq = readl(lcd_irq_base + S3C24XX_LCDINTPND);

    /*判斷是否為中斷掛起狀態*/
    if(lcdirq & S3C2410_LCDINT_FRSYNC)
    {
        /*填充調色板*/
        if (fbvar->palette_ready)
        {
            my2440fb_write_palette(fbvar);
        }

        /*設置幀已插入中斷請求*/
        writel(S3C2410_LCDINT_FRSYNC, lcd_irq_base + S3C24XX_LCDINTPND);
        writel(S3C2410_LCDINT_FRSYNC, lcd_irq_base + S3C24XX_LCDSRCPND);
    }

    return IRQ_HANDLED;
}

/*填充調色板*/
static void my2440fb_write_palette(struct my2440fb_var *fbvar)
{
    unsigned int i;
    void __iomem *regs = fbvar->lcd_base;

    fbvar->palette_ready = 0;

    for (i = 0; i < 256; i++)
    {
        unsigned long ent = fbvar->palette_buffer[i];

        if (ent == PALETTE_BUFF_CLEAR)
        {
            continue;
        }

        writel(ent, regs + S3C2410_TFTPAL(i));

        if (readw(regs + S3C2410_TFTPAL(i)) == ent)
        {
            fbvar->palette_buffer[i] = PALETTE_BUFF_CLEAR;
        }
        else
        {
            fbvar->palette_ready = 1;
        }
    }
}

/*LCD各寄存器進行初始化*/
static int my2440fb_init_registers(struct fb_info *fbinfo)
{
    unsigned long flags;
    void __iomem *tpal;
    void __iomem *lpcsel;

    /*從lcd_fb_probe探測函數設置的私有變量結構體中再獲得LCD相關信息的數據*/
    struct my2440fb_var    *fbvar = fbinfo->par;
    struct s3c2410fb_mach_info *mach_info = fbvar->dev->platform_data;

    /*獲得臨時調色板寄存器基地址，S3C2410_TPAL宏定義在mach-s3c2410/include/mach/regs-lcd.h中。
    注意對於lpcsel這是一個針對三星TFT屏的一個專用寄存器，如果用的不是三星的TFT屏應該不用管它。*/
    tpal = fbvar->lcd_base + S3C2410_TPAL;
    lpcsel = fbvar->lcd_base + S3C2410_LPCSEL;

    /*在修改下面寄存器值之前先屏蔽中斷，將中斷狀態保存到flags中*/
    local_irq_save(flags);

    /*這里就是在上一篇章中講到的把IO端口C和D配置成LCD模式*/
    modify_gpio(S3C2410_GPCUP, mach_info->gpcup, mach_info->gpcup_mask);
    modify_gpio(S3C2410_GPCCON, mach_info->gpccon, mach_info->gpccon_mask);
    modify_gpio(S3C2410_GPDUP, mach_info->gpdup, mach_info->gpdup_mask);
    modify_gpio(S3C2410_GPDCON, mach_info->gpdcon, mach_info->gpdcon_mask);

    /*恢復被屏蔽的中斷*/
    local_irq_restore(flags);

    writel(0x00, tpal);/*臨時調色板寄存器使能禁止*/
    writel(mach_info->lpcsel, lpcsel);/*在上一篇中講到過，它是三星TFT屏的一個寄存器，這里可以不管*/

    return 0;
}

/*該函數實現修改GPIO端口的值，注意第三個參數mask的作用是將要設置的寄存器值先清零*/
static inline void modify_gpio(void __iomem *reg, unsigned long set, unsigned longmask)
{
    unsigned long tmp;

    tmp = readl(reg) & ~mask;
    writel(tmp | set, reg);
}

/*檢查fb_info中的可變參數*/
static int my2440fb_check_var(struct fb_info *fbinfo)
{
    unsigned i;

    /*從lcd_fb_probe探測函數設置的平台數據中再獲得LCD相關信息的數據*/
    struct fb_var_screeninfo *var = &fbinfo->var;/*fb_info中的可變參數*/
    struct my2440fb_var    *fbvar = fbinfo->par;/*在lcd_fb_probe探測函數中設置的私有結構體數據*/
    struct s3c2410fb_mach_info *mach_info = fbvar->dev->platform_data;/*LCD的配置結構體數據，這個配置結構體的賦值在上一篇章的"3. 幀緩沖設備作為平台設備"中*/

    struct s3c2410fb_display *display = NULL;
    struct s3c2410fb_display *default_display = mach_info->displays +mach_info->default_display;
    int type = default_display->type;/*LCD的類型，看上一篇章的"3. 幀緩沖設備作為平台設備"中的type賦值是TFT類型*/

    /*驗證X/Y解析度*/
    if (var->yres == default_display->yres &&
        var->xres == default_display->xres &&
        var->bits_per_pixel == default_display->bpp)
    {
        display = default_display;
    }
    else
    {
        for (i = 0; i < mach_info->num_displays; i++)
        {
            if (type == mach_info->displays[i].type &&
             var->yres == mach_info->displays[i].yres &&
             var->xres == mach_info->displays[i].xres &&
             var->bits_per_pixel == mach_info->displays[i].bpp)
            {
                display = mach_info->displays + i;
                break;
            }
        }
    }

    if (!display)
    {
        return -EINVAL;
    }

    /*配置LCD配置寄存器1中的5-6位(配置成TFT類型)和配置LCD配置寄存器5*/
    fbvar->regs.lcdcon1 = display->type;
    fbvar->regs.lcdcon5 = display->lcdcon5;

    /* 設置屏幕的虛擬解析像素和高度寬度 */
    var->xres_virtual = display->xres;
    var->yres_virtual = display->yres;
    var->height = display->height;
    var->width = display->width;

    /* 設置時鍾像素，行、幀切換值，水平同步、垂直同步長度值 */
    var->pixclock = display->pixclock;
    var->left_margin = display->left_margin;
    var->right_margin = display->right_margin;
    var->upper_margin = display->upper_margin;
    var->lower_margin = display->lower_margin;
    var->vsync_len = display->vsync_len;
    var->hsync_len = display->hsync_len;

    /*設置透明度*/
    var->transp.offset = 0;
    var->transp.length = 0;

    /*根據色位模式(BPP)來設置可變參數中R、G、B的顏色位域。對於這些參數值的設置請參考CPU數據
    手冊中"顯示緩沖區與顯示點對應關系圖"，例如在上一篇章中我就畫出了8BPP和16BPP時的對應關系圖*/
    switch (var->bits_per_pixel)
    {
        case 1:
        case 2:
        case 4:
            var->red.offset  = 0;
            var->red.length  = var->bits_per_pixel;
            var->green       = var->red;
            var->blue        = var->red;
            break;
        case 8:/* 8 bpp 332 */
            if (display->type != S3C2410_LCDCON1_TFT)
            {
                var->red.length     = 3;
                var->red.offset     = 5;
                var->green.length   = 3;
                var->green.offset   = 2;
                var->blue.length    = 2;
                var->blue.offset    = 0;
            }else{
                var->red.offset     = 0;
                var->red.length     = 8;
                var->green          = var->red;
                var->blue           = var->red;
            }
            break;
        case 12:/* 12 bpp 444 */
            var->red.length         = 4;
            var->red.offset         = 8;
            var->green.length       = 4;
            var->green.offset       = 4;
            var->blue.length        = 4;
            var->blue.offset        = 0;
            break;
        case 16:/* 16 bpp */
            if (display->lcdcon5 & S3C2410_LCDCON5_FRM565)
            {
                /* 565 format */
                var->red.offset      = 11;
                var->green.offset    = 5;
                var->blue.offset     = 0;
                var->red.length      = 5;
                var->green.length    = 6;
                var->blue.length     = 5;
            } else {
                /* 5551 format */
                var->red.offset      = 11;
                var->green.offset    = 6;
                var->blue.offset     = 1;
                var->red.length      = 5;
                var->green.length    = 5;
                var->blue.length     = 5;
            }
            break;
        case 32:/* 24 bpp 888 and 8 dummy */
            var->red.length        = 8;
            var->red.offset        = 16;
            var->green.length      = 8;
            var->green.offset      = 8;
            var->blue.length       = 8;
            var->blue.offset       = 0;
            break;
    }

    return 0;
}

/*申請幀緩沖設備fb_info的顯示緩沖區空間*/
static int __init my2440fb_map_video_memory(struct fb_info *fbinfo)
{
    dma_addr_t map_dma;/*用於保存DMA緩沖區總線地址*/
    struct my2440fb_var    *fbvar = fbinfo->par;/*獲得在lcd_fb_probe探測函數中設置的私有結構體數據*/
    unsigned map_size = PAGE_ALIGN(fbinfo->fix.smem_len);/*獲得FrameBuffer緩存的大小, PAGE_ALIGN定義在mm.h中*/

    /*將分配的一個寫合並DMA緩存區設置為LCD屏幕的虛擬地址(對於DMA請參考DMA相關知識)
    dma_alloc_writecombine定義在arch/arm/mm/dma-mapping.c中*/
    fbinfo->screen_base = dma_alloc_writecombine(fbvar->dev, map_size, &map_dma,GFP_KERNEL);

    if (fbinfo->screen_base)
    {
        /*設置這片DMA緩存區的內容為空*/
        memset(fbinfo->screen_base, 0x00, map_size);

        /*將DMA緩沖區總線地址設成fb_info不可變參數中framebuffer緩存的開始位置*/
        fbinfo->fix.smem_start = map_dma;
    }

    return fbinfo->screen_base ? 0 : -ENOMEM;
}

/*釋放幀緩沖設備fb_info的顯示緩沖區空間*/
static inline void my2440fb_unmap_video_memory(struct fb_info *fbinfo)
{
    struct my2440fb_var    *fbvar = fbinfo->par;
    unsigned map_size = PAGE_ALIGN(fbinfo->fix.smem_len);

    /*跟申請DMA的地方想對應*/
    dma_free_writecombine(fbvar->dev, map_size, fbinfo->screen_base, fbinfo->fix.smem_start);
}

/*LCD FrameBuffer設備移除的實現，注意這里使用一個__devexit宏，和lcd_fb_probe接口函數相對應。
  在Linux內核中，使用了大量不同的宏來標記具有不同作用的函數和數據結構，這些宏在include/linux/init.h
  頭文件中定義，編譯器通過這些宏可以把代碼優化放到合適的內存位置，以減少內存占用和提高內核效率。
  __devinit、__devexit就是這些宏之一，在probe()和remove()函數中應該使用__devinit和__devexit宏。
  又當remove()函數使用了__devexit宏時，則在驅動結構體中一定要使用__devexit_p宏來引用remove()，
  所以在第①步中就用__devexit_p來引用lcd_fb_remove接口函數。*/
static int __devexit lcd_fb_remove(struct platform_device *pdev)
{
    struct fb_info *fbinfo = platform_get_drvdata(pdev);
    struct my2440fb_var    *fbvar = fbinfo->par;

    /*從系統中注銷幀緩沖設備*/
    unregister_framebuffer(fbinfo);

    /*停止LCD控制器的工作*/
    my2440fb_lcd_enable(fbvar, 0);

    /*延遲一段時間，因為停止LCD控制器需要一點時間 */
    msleep(1);

    /*釋放幀緩沖設備fb_info的顯示緩沖區空間*/
    my2440fb_unmap_video_memory(fbinfo);

    /*將LCD平台數據清空和釋放fb_info空間資源*/
    platform_set_drvdata(pdev, NULL);
    framebuffer_release(fbinfo);

    /*釋放中斷資源*/
    free_irq(fbvar->lcd_irq_no, fbvar);

    /*釋放時鍾資源*/
    if (fbvar->lcd_clock)
    {
        clk_disable(fbvar->lcd_clock);
        clk_put(fbvar->lcd_clock);
        fbvar->lcd_clock = NULL;
    }

    /*釋放LCD IO空間映射的虛擬內存空間*/
    iounmap(fbvar->lcd_base);

    /*釋放申請的LCD IO端口所占用的IO空間*/
    release_resource(fbvar->lcd_mem);
    kfree(fbvar->lcd_mem);

    return 0;
}

/*停止LCD控制器的工作*/
static void my2440fb_lcd_enable(struct my2440fb_var *fbvar, int enable)
{
    unsigned long flags;

    /*在修改下面寄存器值之前先屏蔽中斷，將中斷狀態保存到flags中*/
    local_irq_save(flags);

    if (enable)
    {
        fbvar->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID;
    }
    else
    {
        fbvar->regs.lcdcon1 &= ~S3C2410_LCDCON1_ENVID;
    }

    writel(fbvar->regs.lcdcon1, fbvar->lcd_base + S3C2410_LCDCON1);

    /*恢復被屏蔽的中斷*/
    local_irq_restore(flags);
}

/*對LCD FrameBuffer平台設備驅動電源管理的支持,CONFIG_PM這個宏定義在內核中*/
#ifdef CONFIG_PM
/*當配置內核時選上電源管理，則平台設備的驅動就支持掛起和恢復功能*/
static int lcd_fb_suspend(struct platform_device *pdev, pm_message_t state)
{
    /*掛起LCD設備，注意這里掛起LCD時並沒有保存LCD控制器的各種狀態，所以在恢復后LCD不會繼續顯示掛起前的內容
     若要繼續顯示掛起前的內容，則要在這里保存LCD控制器的各種狀態，這里就不講這個了，以后講到電源管理再講*/
    struct fb_info *fbinfo = platform_get_drvdata(pdev);
    struct my2440fb_var    *fbvar = fbinfo->par;

    /*停止LCD控制器的工作*/
    my2440fb_lcd_enable(fbvar, 0);

    msleep(1);

    /*停止時鍾*/
    clk_disable(fbvar->lcd_clock);

    return 0;
}

static int lcd_fb_resume(struct platform_device *pdev)
{
    /*恢復掛起的LCD設備*/
    struct fb_info *fbinfo = platform_get_drvdata(pdev);
    struct my2440fb_var    *fbvar = fbinfo->par;

    /*開啟時鍾*/
    clk_enable(fbvar->lcd_clock);

    /*初始化LCD控制器之前要延遲一段時間*/
    msleep(1);

    /*恢復時重新初始化LCD各寄存器*/
    my2440fb_init_registers(fbinfo);

    /*重新激活fb_info中所有的參數配置，該函數定義在第③步中再講*/
    my2440fb_activate_var(fbinfo);

    /*正與掛起時講到的那樣，因為沒保存掛起時LCD控制器的各種狀態，
    所以恢復后就讓LCD顯示空白，該函數定義也在第③步中再講*/
    my2440fb_blank(FB_BLANK_UNBLANK, fbinfo);

    return 0;
}
#else
/*如果配置內核時沒選上電源管理,則平台設備的驅動就不支持掛起和恢復功能,這兩個函數也就無需實現了*/
#define lcd_fb_suspend    NULL
#define lcd_fb_resume    NULL
#endif

fbinfo->pseudo_palette = &fbvar->pseudo_pal;

③、幀緩沖設備驅動對底層硬件操作的函數接口實現(即：my2440fb_ops的實現)：

/*Framebuffer底層硬件操作各接口函數*/ static struct fb_ops my2440fb_ops = { .owner = THIS_MODULE, .fb_check_var = my2440fb_check_var,/*第②步中已實現*/ .fb_set_par = my2440fb_set_par,/*設置fb_info中的參數，主要是LCD的顯示模式*/ .fb_blank = my2440fb_blank,/*顯示空白(即：LCD開關控制)*/ .fb_setcolreg = my2440fb_setcolreg,/*設置顏色表*/ /*以下三個函數是可選的，主要是提供fb_console的支持，在內核中已經實現，這里直接調用即可*/ .fb_fillrect = cfb_fillrect,/*定義在drivers/video/cfbfillrect.c中*/ .fb_copyarea = cfb_copyarea,/*定義在drivers/video/cfbcopyarea.c中*/ .fb_imageblit = cfb_imageblit,/*定義在drivers/video/cfbimgblt.c中*/ }; /*設置fb_info中的參數，這里根據用戶設置的可變參數var調整固定參數fix*/ static int my2440fb_set_par(struct fb_info *fbinfo) { /*獲得fb_info中的可變參數*/ struct fb_var_screeninfo *var = &fbinfo->var; /*判斷可變參數中的色位模式，根據色位模式來設置色彩模式*/ switch (var->bits_per_pixel) { case 32: case 16: case 12:/*12BPP時，設置為真彩色(分成紅、綠、藍三基色)*/ fbinfo->fix.visual = FB_VISUAL_TRUECOLOR; break; case 1:/*1BPP時，設置為黑白色(分黑、白兩種色，FB_VISUAL_MONO01代表黑，FB_VISUAL_MONO10代表白)*/ fbinfo->fix.visual = FB_VISUAL_MONO01; break; default:/*默認設置為偽彩色，采用索引顏色顯示*/ fbinfo->fix.visual = FB_VISUAL_PSEUDOCOLOR; break; } /*設置fb_info中固定參數中一行的字節數，公式：1行字節數=(1行像素個數*每像素位數BPP)/8 */ fbinfo->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8; /*修改以上參數后，重新激活fb_info中的參數配置(即：使修改后的參數在硬件上生效)*/ my2440fb_activate_var(fbinfo); return 0; } /*重新激活fb_info中的參數配置*/ static void my2440fb_activate_var(struct fb_info *fbinfo) { /*獲得結構體變量*/ struct my2440fb_var *fbvar = fbinfo->par; void __iomem *regs = fbvar->lcd_base; /*獲得fb_info可變參數*/ struct fb_var_screeninfo *var = &fbinfo->var; /*計算LCD控制寄存器1中的CLKVAL值, 根據數據手冊中該寄存器的描述，計算公式如下： * STN屏：VCLK = HCLK / (CLKVAL * 2), CLKVAL要求>= 2 * TFT屏：VCLK = HCLK / [(CLKVAL + 1) * 2], CLKVAL要求>= 0*/ int clkdiv = my2440fb_calc_pixclk(fbvar, var->pixclock) / 2; /*獲得屏幕的類型*/ int type = fbvar->regs.lcdcon1 & S3C2410_LCDCON1_TFT; if (type == S3C2410_LCDCON1_TFT) { /*根據數據手冊按照TFT屏的要求配置LCD控制寄存器1-5*/ my2440fb_config_tft_lcd_regs(fbinfo, &fbvar->regs); --clkdiv; if (clkdiv < 0) { clkdiv = 0; } } else { /*根據數據手冊按照STN屏的要求配置LCD控制寄存器1-5*/ my2440fb_config_stn_lcd_regs(fbinfo, &fbvar->regs); if (clkdiv < 2) { clkdiv = 2; } } /*設置計算的LCD控制寄存器1中的CLKVAL值*/ fbvar->regs.lcdcon1 |= S3C2410_LCDCON1_CLKVAL(clkdiv); /*將各參數值寫入LCD控制寄存器1-5中*/ writel(fbvar->regs.lcdcon1 & ~S3C2410_LCDCON1_ENVID, regs +S3C2410_LCDCON1); writel(fbvar->regs.lcdcon2, regs + S3C2410_LCDCON2); writel(fbvar->regs.lcdcon3, regs + S3C2410_LCDCON3); writel(fbvar->regs.lcdcon4, regs + S3C2410_LCDCON4); writel(fbvar->regs.lcdcon5, regs + S3C2410_LCDCON5); /*配置幀緩沖起始地址寄存器1-3*/ my2440fb_set_lcdaddr(fbinfo); fbvar->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID, writel(fbvar->regs.lcdcon1, regs + S3C2410_LCDCON1); } /*計算LCD控制寄存器1中的CLKVAL值*/ static unsigned int my2440fb_calc_pixclk(struct my2440fb_var *fbvar, unsignedlong pixclk) { /*獲得LCD的時鍾*/ unsigned long clk = clk_get_rate(fbvar->lcd_clock); /* 像素時鍾單位是皮秒，而時鍾的單位是赫茲，所以計算公式為： * Hz -> picoseconds is / 10^-12 */ unsigned long long div = (unsigned long long)clk * pixclk; div >>= 12; /* div / 2^12 */ do_div(div, 625 * 625UL * 625); /* div / 5^12, do_div宏定義在asm/div64.h中*/ return div; } /*根據數據手冊按照TFT屏的要求配置LCD控制寄存器1-5*/ static void my2440fb_config_tft_lcd_regs(const struct fb_info *fbinfo, structs3c2410fb_hw *regs) { const struct my2440fb_var *fbvar = fbinfo->par; const struct fb_var_screeninfo *var = &fbinfo->var; /*根據色位模式設置LCD控制寄存器1和5，參考數據手冊*/ switch (var->bits_per_pixel) { case 1:/*1BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT1BPP; break; case 2:/*2BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT2BPP; break; case 4:/*4BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT4BPP; break; case 8:/*8BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT8BPP; regs->lcdcon5 |= S3C2410_LCDCON5_BSWP |S3C2410_LCDCON5_FRM565; regs->lcdcon5 &= ~S3C2410_LCDCON5_HWSWP; break; case 16:/*16BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT16BPP; regs->lcdcon5 &= ~S3C2410_LCDCON5_BSWP; regs->lcdcon5 |= S3C2410_LCDCON5_HWSWP; break; case 32:/*32BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT24BPP; regs->lcdcon5 &= ~(S3C2410_LCDCON5_BSWP |S3C2410_LCDCON5_HWSWP | S3C2410_LCDCON5_BPP24BL); break; default:/*無效的BPP*/ dev_err(fbvar->dev, "invalid bpp %d/n", var->bits_per_pixel); } /*設置LCD配置寄存器2、3、4*/ regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1) | S3C2410_LCDCON2_VBPD(var->upper_margin - 1) | S3C2410_LCDCON2_VFPD(var->lower_margin - 1) | S3C2410_LCDCON2_VSPW(var->vsync_len - 1); regs->lcdcon3 = S3C2410_LCDCON3_HBPD(var->right_margin - 1) | S3C2410_LCDCON3_HFPD(var->left_margin - 1) | S3C2410_LCDCON3_HOZVAL(var->xres - 1); regs->lcdcon4 = S3C2410_LCDCON4_HSPW(var->hsync_len - 1); } /*根據數據手冊按照STN屏的要求配置LCD控制寄存器1-5*/ static void my2440fb_config_stn_lcd_regs(const struct fb_info *fbinfo, structs3c2410fb_hw *regs) { const struct my2440fb_var *fbvar = fbinfo->par; const struct fb_var_screeninfo *var = &fbinfo->var; int type = regs->lcdcon1 & ~S3C2410_LCDCON1_TFT; int hs = var->xres >> 2; unsigned wdly = (var->left_margin >> 4) - 1; unsigned wlh = (var->hsync_len >> 4) - 1; if (type != S3C2410_LCDCON1_STN4) { hs >>= 1; } /*根據色位模式設置LCD控制寄存器1，參考數據手冊*/ switch (var->bits_per_pixel) { case 1:/*1BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN1BPP; break; case 2:/*2BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN2GREY; break; case 4:/*4BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN4GREY; break; case 8:/*8BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN8BPP; hs *= 3; break; case 12:/*12BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN12BPP; hs *= 3; break; default:/*無效的BPP*/ dev_err(fbvar->dev, "invalid bpp %d/n", var->bits_per_pixel); } /*設置LCD配置寄存器2、3、4, 參考數據手冊*/ if (wdly > 3) wdly = 3; if (wlh > 3) wlh = 3; regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1); regs->lcdcon3 = S3C2410_LCDCON3_WDLY(wdly) | S3C2410_LCDCON3_LINEBLANK(var->right_margin / 8) | S3C2410_LCDCON3_HOZVAL(hs - 1); regs->lcdcon4 = S3C2410_LCDCON4_WLH(wlh); } /*配置幀緩沖起始地址寄存器1-3，參考數據手冊*/ static void my2440fb_set_lcdaddr(struct fb_info *fbinfo) { unsigned long saddr1, saddr2, saddr3; struct my2440fb_var *fbvar = fbinfo->par; void __iomem *regs = fbvar->lcd_base; saddr1 = fbinfo->fix.smem_start >> 1; saddr2 = fbinfo->fix.smem_start; saddr2 += fbinfo->fix.line_length * fbinfo->var.yres; saddr2 >>= 1; saddr3 = S3C2410_OFFSIZE(0) | S3C2410_PAGEWIDTH((fbinfo->fix.line_length/ 2) & 0x3ff); writel(saddr1, regs + S3C2410_LCDSADDR1); writel(saddr2, regs + S3C2410_LCDSADDR2); writel(saddr3, regs + S3C2410_LCDSADDR3); } /*顯示空白，blank mode有5種模式，定義在fb.h中，是一個枚舉*/ static int my2440fb_blank(int blank_mode, struct fb_info *fbinfo) { struct my2440fb_var *fbvar = fbinfo->par; void __iomem *regs = fbvar->lcd_base; /*根據顯示空白的模式來設置LCD是開啟還是停止*/ if (blank_mode == FB_BLANK_POWERDOWN) { my2440fb_lcd_enable(fbvar, 0);/*在第②步中定義*/ } else { my2440fb_lcd_enable(fbvar, 1);/*在第②步中定義*/ } /*根據顯示空白的模式來控制臨時調色板寄存器*/ if (blank_mode == FB_BLANK_UNBLANK) { /*臨時調色板寄存器無效*/ writel(0x0, regs + S3C2410_TPAL); } else { /*臨時調色板寄存器有效*/ writel(S3C2410_TPAL_EN, regs + S3C2410_TPAL); } return 0; } /*設置顏色表*/ static int my2440fb_setcolreg(unsigned regno,unsigned red,unsignedgreen,unsigned blue,unsigned transp,struct fb_info *fbinfo) { unsigned int val; struct my2440fb_var *fbvar = fbinfo->par; void __iomem *regs = fbvar->lcd_base; switch (fbinfo->fix.visual) { case FB_VISUAL_TRUECOLOR: /*真彩色*/ if (regno < 16) { u32 *pal = fbinfo->pseudo_palette; val = chan_to_field(red, &fbinfo->var.red); val |= chan_to_field(green, &fbinfo->var.green); val |= chan_to_field(blue, &fbinfo->var.blue); pal[regno] = val; } break; case FB_VISUAL_PSEUDOCOLOR: /*偽彩色*/ if (regno < 256) { val = (red >> 0) & 0xf800; val |= (green >> 5) & 0x07e0; val |= (blue >> 11) & 0x001f; writel(val, regs + S3C2410_TFTPAL(regno)); /*修改調色板*/ schedule_palette_update(fbvar, regno, val); } break; default: return 1; } return 0; } static inline unsigned int chan_to_field(unsigned int chan, struct fb_bitfield *bf) { chan &= 0xffff; chan >>= 16 - bf->length; return chan << bf->offset; } /*修改調色板*/ static void schedule_palette_update(struct my2440fb_var *fbvar, unsigned intregno, unsigned int val) { unsigned long flags; unsigned long irqen; /*LCD中斷掛起寄存器基地址*/ void __iomem *lcd_irq_base = fbvar->lcd_base + S3C2410_LCDINTBASE; /*在修改中斷寄存器值之前先屏蔽中斷，將中斷狀態保存到flags中*/ local_irq_save(flags); fbvar->palette_buffer[regno] = val; /*判斷調色板是否准備就像*/ if (!fbvar->palette_ready) { fbvar->palette_ready = 1; /*使能中斷屏蔽寄存器*/ irqen = readl(lcd_irq_base + S3C24XX_LCDINTMSK); irqen &= ~S3C2410_LCDINT_FRSYNC; writel(irqen, lcd_irq_base + S3C24XX_LCDINTMSK); } /*恢復被屏蔽的中斷*/ local_irq_restore(flags); }

五、從整體上再描述一下FrameBuffer設備驅動實例代碼的結構：

1、在第①部分代碼中主要做的事情有：

a.將LCD設備注冊到系統平台設備中；

b.定義LCD平台設備結構體lcd_fb_driver。

2、在第②部分代碼中主要做的事情有：

a.獲取和設置LCD平台設備的各種資源；

b.分配fb_info結構體空間；

c.初始化fb_info結構體中的各參數；

d.初始化LCD控制器；

e.檢查fb_info中可變參數；

f.申請幀緩沖設備的顯示緩沖區空間；

g.注冊fb_info。

3、在第③部分代碼中主要做的事情有：

a.實現對fb_info相關參數進行檢查的硬件接口函數；

b.實現對LCD顯示模式進行設定的硬件接口函數；

c.實現對LCD顯示開關(空白)的硬件接口函數等。

memcpy

//這里就是將內核中定義的s3c2410fb_mach_info結構體數據保存到LCD平台數據中，所以在寫驅動的時候就可以直接在平台數據中獲取s3c2410fb_mach_info結構體的數據(即LCD各種參數信息)進行操作 s3c_device_lcd.dev.platform_data = npd; } else { printk(KERN_ERR "no memory for LCD platform data/n"); } }

//S3C2440初始化函數 static void __init smdk2440_machine_init(void) {

//調用該函數將上面定義的LCD硬件信息保存到平台數據中 s3c24xx_fb_set_platdata(&smdk2440_fb_info); s3c_i2c0_set_platdata(NULL); platform_add_devices(smdk2440_devices, ARRAY_SIZE(smdk2440_devices)); smdk_machine_init(); }

/* LCD Controller */

//LCD控制器的資源信息 static struct resource s3c_lcd_resource[] = { [0] = { .start = S3C24XX_PA_LCD, //控制器IO端口開始地址 .end = S3C24XX_PA_LCD + S3C24XX_SZ_LCD - 1,//控制器IO端口結束地址 .flags = IORESOURCE_MEM,//標識為LCD控制器IO端口，在驅動中引用這個就表示引用IO端口 }, [1] = { .start = IRQ_LCD,//LCD中斷 .end = IRQ_LCD, .flags = IORESOURCE_IRQ,//標識為LCD中斷 } }; static u64 s3c_device_lcd_dmamask = 0xffffffffUL; struct platform_device s3c_device_lcd = { .name = "s3c2410-lcd",//作為平台設備的LCD設備名 .id = -1, .num_resources = ARRAY_SIZE(s3c_lcd_resource),//資源數量 .resource = s3c_lcd_resource,//引用上面定義的資源 .dev = { .dma_mask = &s3c_device_lcd_dmamask, .coherent_dma_mask = 0xffffffffUL } }; EXPORT_SYMBOL(s3c_device_lcd);//導出定義的LCD平台設備，好在mach-smdk2440.c的smdk2440_devices[]中添加到平台設備列表中

struct fb_info { int node; int flags; struct fb_var_screeninfo var;/*LCD可變參數結構體*/ struct fb_fix_screeninfo fix;/*LCD固定參數結構體*/ struct fb_monspecs monspecs; /*LCD顯示器標准*/ struct work_struct queue; /*幀緩沖事件隊列*/ struct fb_pixmap pixmap; /*圖像硬件mapper*/ struct fb_pixmap sprite; /*光標硬件mapper*/ struct fb_cmap cmap; /*當前的顏色表*/ struct fb_videomode *mode; /*當前的顯示模式*/ #ifdef CONFIG_FB_BACKLIGHT struct backlight_device *bl_dev;/*對應的背光設備*/ struct mutex bl_curve_mutex; u8 bl_curve[FB_BACKLIGHT_LEVELS];/*背光調整*/ #endif #ifdef CONFIG_FB_DEFERRED_IO struct delayed_work deferred_work; struct fb_deferred_io *fbdefio; #endif struct fb_ops *fbops; /*對底層硬件操作的函數指針*/ struct device *device; struct device *dev; /*fb設備*/ int class_flag; #ifdef CONFIG_FB_TILEBLITTING struct fb_tile_ops *tileops; /*圖塊Blitting*/ #endif char __iomem *screen_base; /*虛擬基地址*/ unsigned long screen_size; /*LCD IO映射的虛擬內存大小*/ void *pseudo_palette; /*偽16色顏色表*/ #define FBINFO_STATE_RUNNING 0 #define FBINFO_STATE_SUSPENDED 1 u32 state; /*LCD的掛起或恢復狀態*/ void *fbcon_par; void *par; };

其中，比較重要的成員有struct fb_var_screeninfo var、struct fb_fix_screeninfo fix和structfb_ops *fbops，他們也都是結構體。下面我們一個一個的來看。

fb_var_screeninfo結構體主要記錄用戶可以修改的控制器的參數，比如屏幕的分辨率和每個像素的比特數等，該結構體定義如下：

而fb_fix_screeninfo結構體又主要記錄用戶不可以修改的控制器的參數，比如屏幕緩沖區的物理地址和長度等，該結構體的定義如下：

struct fb_fix_screeninfo { char id[16]; /*字符串形式的標示符 */ unsigned long smem_start; /*fb緩存的開始位置 */ __u32 smem_len; /*fb緩存的長度 */ __u32 type; /*看FB_TYPE_* */ __u32 type_aux; /*分界*/ __u32 visual; /*看FB_VISUAL_* */ __u16 xpanstep; /*如果沒有硬件panning就賦值為0 */ __u16 ypanstep; /*如果沒有硬件panning就賦值為0 */ __u16 ywrapstep; /*如果沒有硬件ywrap就賦值為0 */ __u32 line_length; /*一行的字節數 */ unsigned long mmio_start; /*內存映射IO的開始位置*/ __u32 mmio_len; /*內存映射IO的長度*/ __u32 accel; __u16 reserved[3]; /*保留*/ };

struct fb_var_screeninfo { __u32 xres; /*可見屏幕一行有多少個像素點*/ __u32 yres; /*可見屏幕一列有多少個像素點*/ __u32 xres_virtual; /*虛擬屏幕一行有多少個像素點*/ __u32 yres_virtual; /*虛擬屏幕一列有多少個像素點*/ __u32 xoffset; /*虛擬到可見屏幕之間的行偏移*/ __u32 yoffset; /*虛擬到可見屏幕之間的列偏移*/ __u32 bits_per_pixel; /*每個像素的位數即BPP*/ __u32 grayscale; /*非0時，指的是灰度*/ struct fb_bitfield red; /*fb緩存的R位域*/ struct fb_bitfield green; /*fb緩存的G位域*/ struct fb_bitfield blue; /*fb緩存的B位域*/ struct fb_bitfield transp; /*透明度*/ __u32 nonstd; /* != 0 非標准像素格式*/ __u32 activate; __u32 height; /*高度*/ __u32 width; /*寬度*/ __u32 accel_flags; /*定時：除了pixclock本身外，其他的都以像素時鍾為單位*/ __u32 pixclock; /*像素時鍾(皮秒)*/ __u32 left_margin; /*行切換，從同步到繪圖之間的延遲*/ __u32 right_margin; /*行切換，從繪圖到同步之間的延遲*/ __u32 upper_margin; /*幀切換，從同步到繪圖之間的延遲*/ __u32 lower_margin; /*幀切換，從繪圖到同步之間的延遲*/ __u32 hsync_len; /*水平同步的長度*/ __u32 vsync_len; /*垂直同步的長度*/ __u32 sync; __u32 vmode; __u32 rotate; __u32 reserved[5]; /*保留*/ };

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