一、設備樹文件編寫
1 spi_master: spi_master 2 { 3 #address-cells = <1>; 4 #size-cells = <0>; 5 compatible = "spi_master"; 6 io_phy_addr = <0x1f000000>; 7 banks = <0x1110>,<0x1111>,<0x1038>,<0x101E>; 8 interrupts = <GIC_SPI INT_IRQ_MSPI_0 IRQ_TYPE_LEVEL_HIGH>,<GIC_SPI INT_IRQ_MSPI_1 IRQ_TYPE_LEVEL_HIGH>; 9 spi0_mode = <1>; 10 spi1_mode = <3>; 11 status = "okay"; 12 13 spi_device: spi_device 14 { 15 compatible = "spi_device"; 16 reg = <0x0>; 17 spi-max-frequency = <10000000>; 18 status = "okay"; 19 }; 20 };
如上DTS文件片段，SPI Device 節點必須定義在 SPI Master 節點下，其中 compatible 屬性和 reg 屬性，以上 compatible 屬性用於匹配對應的 Driver 程序，reg 屬性用於指定使用的 SPI Master 的編號，SPI 相關設備樹文件識別見下文講解。
二、代碼流程
匹配設備樹文件在SPI子系統中有兩個地方：在 spi_register_master() 中匹配和在 device register 時通過內核的通知鏈（notifier_block）來調用設備樹匹配相關程序。
在 spi_register_master() 中匹配：
1 //driver/spi/spi.c 2 int spi_register_master(struct spi_master *master) 3 { 4 static atomic_t dyn_bus_id = ATOMIC_INIT((1<<15) - 1); 5 struct device *dev = master->dev.parent; 6 struct boardinfo *bi; 7 int status = -ENODEV; 8 int dynamic = 0; 9 10 if (!dev) 11 return -ENODEV; 12 13 status = of_spi_register_master(master); 14 if (status) 15 return status; 16 17 /* even if it's just one always-selected device, there must 18 * be at least one chipselect 19 */ 20 if (master->num_chipselect == 0) 21 return -EINVAL; 22 23 if ((master->bus_num < 0) && master->dev.of_node) 24 master->bus_num = of_alias_get_id(master->dev.of_node, "spi"); 25 26 /* convention: dynamically assigned bus IDs count down from the max */ 27 if (master->bus_num < 0) { 28 /* FIXME switch to an IDR based scheme, something like 29 * I2C now uses, so we can't run out of "dynamic" IDs 30 */ 31 master->bus_num = atomic_dec_return(&dyn_bus_id); 32 dynamic = 1; 33 } 34 35 INIT_LIST_HEAD(&master->queue); 36 spin_lock_init(&master->queue_lock); 37 spin_lock_init(&master->bus_lock_spinlock); 38 mutex_init(&master->bus_lock_mutex); 39 mutex_init(&master->io_mutex); 40 master->bus_lock_flag = 0; 41 init_completion(&master->xfer_completion); 42 if (!master->max_dma_len) 43 master->max_dma_len = INT_MAX; 44 45 /* register the device, then userspace will see it. 46 * registration fails if the bus ID is in use. 47 */ 48 dev_set_name(&master->dev, "spi%u", master->bus_num); 49 status = device_add(&master->dev); 50 if (status < 0) 51 goto done; 52 dev_dbg(dev, "registered master %s%s\n", dev_name(&master->dev), 53 dynamic ? " (dynamic)" : ""); 54 55 /* If we're using a queued driver, start the queue */ 56 if (master->transfer) 57 dev_info(dev, "master is unqueued, this is deprecated\n"); 58 else { 59 status = spi_master_initialize_queue(master); 60 if (status) { 61 device_del(&master->dev); 62 goto done; 63 } 64 } 65 /* add statistics */ 66 spin_lock_init(&master->statistics.lock); 67 68 mutex_lock(&board_lock); 69 list_add_tail(&master->list, &spi_master_list); 70 list_for_each_entry(bi, &board_list, list) 71 spi_match_master_to_boardinfo(master, &bi->board_info); 72 mutex_unlock(&board_lock); 73 74 /* Register devices from the device tree and ACPI */ 75 of_register_spi_devices(master); // 設備樹匹配操作 76 acpi_register_spi_devices(master); 77 done: 78 return status; 79 }
1 //driver/spi/spi.c 2 static void of_register_spi_devices(struct spi_master *master) 3 { 4 struct spi_device *spi; 5 struct device_node *nc; 6 7 if (!master->dev.of_node) 8 return; 9 10 for_each_available_child_of_node(master->dev.of_node, nc) { 11 if (of_node_test_and_set_flag(nc, OF_POPULATED)) 12 continue; 13 spi = of_register_spi_device(master, nc); // 設備樹匹配操作 14 if (IS_ERR(spi)) { 15 dev_warn(&master->dev, "Failed to create SPI device for %s\n", 16 nc->full_name); 17 of_node_clear_flag(nc, OF_POPULATED); 18 } 19 } 20 }
在 device register 時匹配：
1 //driver/spi/spi.c 2 static int __init spi_init(void) 3 { 4 int status; 5 6 buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL); 7 if (!buf) { 8 status = -ENOMEM; 9 goto err0; 10 } 11 12 status = bus_register(&spi_bus_type); 13 if (status < 0) 14 goto err1; 15 16 status = class_register(&spi_master_class); 17 if (status < 0) 18 goto err2; 19 20 if (IS_ENABLED(CONFIG_OF_DYNAMIC)) 21 WARN_ON(of_reconfig_notifier_register(&spi_of_notifier)); 22 if (IS_ENABLED(CONFIG_ACPI)) 23 WARN_ON(acpi_reconfig_notifier_register(&spi_acpi_notifier)); 24 25 return 0; 26 27 err2: 28 bus_unregister(&spi_bus_type); 29 err1: 30 kfree(buf); 31 buf = NULL; 32 err0: 33 return status; 34 } 35 36 postcore_initcall(spi_init);
在 device register 時，需配置 CONFIG_OF_DYNAMIC 宏以開啟動態匹配才能夠使用設備樹添加設備，該宏在 menuconfig/Device Drivers/Device Tree and Open Firmware support 中開啟，如下圖：
1 //driver/spi/spi.c 2 static struct notifier_block spi_of_notifier = { 3 .notifier_call = of_spi_notify, 4 }; 5 6 static int of_spi_notify(struct notifier_block *nb, unsigned long action, 7 void *arg) 8 { 9 struct of_reconfig_data *rd = arg; 10 struct spi_master *master; 11 struct spi_device *spi; 12 13 switch (of_reconfig_get_state_change(action, arg)) { 14 case OF_RECONFIG_CHANGE_ADD: 15 master = of_find_spi_master_by_node(rd->dn->parent); 16 if (master == NULL) 17 return NOTIFY_OK; /* not for us */ 18 19 if (of_node_test_and_set_flag(rd->dn, OF_POPULATED)) { 20 put_device(&master->dev); 21 return NOTIFY_OK; 22 } 23 24 spi = of_register_spi_device(master, rd->dn); // 設備樹匹配操作 25 put_device(&master->dev); 26 27 if (IS_ERR(spi)) { 28 pr_err("%s: failed to create for '%s'\n", 29 __func__, rd->dn->full_name); 30 of_node_clear_flag(rd->dn, OF_POPULATED); 31 return notifier_from_errno(PTR_ERR(spi)); 32 } 33 break; 34 35 case OF_RECONFIG_CHANGE_REMOVE: 36 /* already depopulated? */ 37 if (!of_node_check_flag(rd->dn, OF_POPULATED)) 38 return NOTIFY_OK; 39 40 /* find our device by node */ 41 spi = of_find_spi_device_by_node(rd->dn); 42 if (spi == NULL) 43 return NOTIFY_OK; /* no? not meant for us */ 44 45 /* unregister takes one ref away */ 46 spi_unregister_device(spi); 47 48 /* and put the reference of the find */ 49 put_device(&spi->dev); 50 break; 51 } 52 53 return NOTIFY_OK; 54 }
1 //driver/spi/spi.c 2 static struct spi_device * 3 of_register_spi_device(struct spi_master *master, struct device_node *nc) 4 { 5 struct spi_device *spi; 6 int rc; 7 u32 value; 8 9 /* Alloc an spi_device */ 10 spi = spi_alloc_device(master); 11 if (!spi) { 12 dev_err(&master->dev, "spi_device alloc error for %s\n", 13 nc->full_name); 14 rc = -ENOMEM; 15 goto err_out; 16 } 17 18 /* Select device driver */ 19 rc = of_modalias_node(nc, spi->modalias, 20 sizeof(spi->modalias)); 21 if (rc < 0) { 22 dev_err(&master->dev, "cannot find modalias for %s\n", 23 nc->full_name); 24 goto err_out; 25 } 26 27 /* Device address */ 28 rc = of_property_read_u32(nc, "reg", &value); 29 if (rc) { 30 dev_err(&master->dev, "%s has no valid 'reg' property (%d)\n", 31 nc->full_name, rc); 32 goto err_out; 33 } 34 spi->chip_select = value; 35 36 /* Mode (clock phase/polarity/etc.) */ 37 if (of_find_property(nc, "spi-cpha", NULL)) 38 spi->mode |= SPI_CPHA; 39 if (of_find_property(nc, "spi-cpol", NULL)) 40 spi->mode |= SPI_CPOL; 41 if (of_find_property(nc, "spi-cs-high", NULL)) 42 spi->mode |= SPI_CS_HIGH; 43 if (of_find_property(nc, "spi-3wire", NULL)) 44 spi->mode |= SPI_3WIRE; 45 if (of_find_property(nc, "spi-lsb-first", NULL)) 46 spi->mode |= SPI_LSB_FIRST; 47 48 /* Device DUAL/QUAD mode */ 49 if (!of_property_read_u32(nc, "spi-tx-bus-width", &value)) { 50 switch (value) { 51 case 1: 52 break; 53 case 2: 54 spi->mode |= SPI_TX_DUAL; 55 break; 56 case 4: 57 spi->mode |= SPI_TX_QUAD; 58 break; 59 default: 60 dev_warn(&master->dev, 61 "spi-tx-bus-width %d not supported\n", 62 value); 63 break; 64 } 65 } 66 67 if (!of_property_read_u32(nc, "spi-rx-bus-width", &value)) { 68 switch (value) { 69 case 1: 70 break; 71 case 2: 72 spi->mode |= SPI_RX_DUAL; 73 break; 74 case 4: 75 spi->mode |= SPI_RX_QUAD; 76 break; 77 default: 78 dev_warn(&master->dev, 79 "spi-rx-bus-width %d not supported\n", 80 value); 81 break; 82 } 83 } 84 85 /* Device speed */ 86 rc = of_property_read_u32(nc, "spi-max-frequency", &value); 87 if (rc) { 88 dev_err(&master->dev, "%s has no valid 'spi-max-frequency' property (%d)\n", 89 nc->full_name, rc); 90 goto err_out; 91 } 92 spi->max_speed_hz = value; 93 94 /* Store a pointer to the node in the device structure */ 95 of_node_get(nc); 96 spi->dev.of_node = nc; 97 98 /* Register the new device */ 99 rc = spi_add_device(spi); 100 if (rc) { 101 dev_err(&master->dev, "spi_device register error %s\n", 102 nc->full_name); 103 goto err_of_node_put; 104 } 105 106 return spi; 107 108 err_of_node_put: 109 of_node_put(nc); 110 err_out: 111 spi_dev_put(spi); 112 return ERR_PTR(rc); 113 }
end