內核版本：3.10.92
內核3.1引入了一套新的API機制：regmap，主要為I2C，SPI，IRQ等操作提供統一接口，提高代碼可重用性，減少重復邏輯。
以I2C為例：
要讓設備跟I2C通信，以前的辦法是調用i2c_transfer接口，其實regmap最終還是調用到i2c_transfer，只不過中間加了一層緩沖，這樣統一了接口，減少了底層I/O的操作次數。
在初始化之前，要先填充regmap_config結構體。
先看看定義：
struct regmap_config {
const char *name;
int reg_bits;//寄存器地址位數，必須配置
int reg_stride;
int pad_bits;//寄存器和值之間的填充位數
int val_bits;//寄存器值的位數，必須配置
bool (*writeable_reg)(struct device *dev, unsigned int reg);
bool (*readable_reg)(struct device *dev, unsigned int reg);
bool (*volatile_reg)(struct device *dev, unsigned int reg);
bool (*precious_reg)(struct device *dev, unsigned int reg);
regmap_lock lock;
regmap_unlock unlock;
void *lock_arg;
int (*reg_read)(void *context, unsigned int reg, unsigned int *val);
int (*reg_write)(void *context, unsigned int reg, unsigned int val);
bool fast_io;
unsigned int max_register;
const struct regmap_access_table *wr_table;
const struct regmap_access_table *rd_table;
const struct regmap_access_table *volatile_table;
const struct regmap_access_table *precious_table;
const struct reg_default *reg_defaults;
unsigned int num_reg_defaults;
enum regcache_type cache_type;
const void *reg_defaults_raw;
unsigned int num_reg_defaults_raw;
u8 read_flag_mask;
u8 write_flag_mask;
bool use_single_rw;
enum regmap_endian reg_format_endian;
enum regmap_endian val_format_endian;
const struct regmap_range_cfg *ranges;
unsigned int num_ranges;
};
注冊：
struct regmap *devm_regmap_init_i2c(struct i2c_client *i2c,
const struct regmap_config *config)
讀寫I2C：
int regmap_read(struct regmap *map, unsigned int reg, unsigned int *val)；//讀取reg中的值，保存在val中
int regmap_raw_read(struct regmap *map, unsigned int reg, void *val,
size_t val_len)； //從reg中讀取val_len長度的數據，保存在val中
int regmap_write(struct regmap *map, unsigned int reg, unsigned int val)；//將val寫入到reg中
int regmap_raw_write(struct regmap *map, unsigned int reg,
const void *val, size_t val_len)；//將val寫入到reg中，val長度為val_len
int regmap_update_bits(struct regmap *map, unsigned int reg,
unsigned int mask, unsigned int val)//更新reg中指定的位
看下注冊過程：
regmap_init_i2c -> //regmap-i2c.c
regmap_init-> //多了兩個參數，最重要是第二個regmap_bus regmap_i2c，實現了I2C的讀寫，SPI同理
map->reg_read = _regmap_bus_read; //綁定讀函數
map->reg_write = _regmap_bus_raw_write; //綁定寫函數
看下讀寫過程：
讀：
regmap_read ->
_regmap_read ->
map->reg_read -> //初始化時已經綁定_regmap_bus_read
_regmap_bus_read->
_regmap_raw_read ->
map->bus->read //調用regmap-i2c.c中實現的regmap_i2c.read
寫：
regmap_write->
_regmap_write ->
map->reg_write -> //初始化時已經綁定_regmap_bus_raw_write
_regmap_bus_raw_write->
_regmap_raw_write->
map->bus->write //調用regmap-i2c.c中實現的regmap_i2c.write
最后看看regmap-i2c.c吧
static int regmap_i2c_write(void *context, const void *data, size_t count)
{
struct device *dev = context;
struct i2c_client *i2c = to_i2c_client(dev);
int ret;
ret = i2c_master_send(i2c, data, count);
if (ret == count)
return 0;
else if (ret < 0)
return ret;
else
return -EIO;
}
static int regmap_i2c_read(void *context,
const void *reg, size_t reg_size,
void *val, size_t val_size)
{
struct device *dev = context;
struct i2c_client *i2c = to_i2c_client(dev);
struct i2c_msg xfer[2];
int ret;
xfer[0].addr = i2c->addr;
xfer[0].flags = 0;
xfer[0].len = reg_size;
xfer[0].buf = (void *)reg;
#ifdef CONFIG_I2C_ROCKCHIP_COMPAT
xfer[0].scl_rate = 100*1000;
#endif
xfer[1].addr = i2c->addr;
xfer[1].flags = I2C_M_RD;
xfer[1].len = val_size;
xfer[1].buf = val;
#ifdef CONFIG_I2C_ROCKCHIP_COMPAT
xfer[1].scl_rate = 100*1000;
#endif
ret = i2c_transfer(i2c->adapter, xfer, 2);
if (ret == 2)
return 0;
else if (ret < 0)
return ret;
else
return -EIO;
}
熟悉吧，跟我們之前調用I2C的方法是一樣的。
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版權聲明：本文為CSDN博主「板磚先生」的原創文章，遵循 CC 4.0 BY-SA 版權協議，轉載請附上原文出處鏈接及本聲明。
原文鏈接：https://blog.csdn.net/heabby2010/article/details/79063949