【linux设备模型】之platform设备驱动
一、platform总线、设备和驱动
platform是一种虚拟总线，对应的设备称为platform_device，对应的驱动称为platform_driver。
platform_device定义在<linux/platform_device.h>中：
1 struct platform_device {
2 const char * name;
3 int id;
4 struct device dev;
5 u32 num_resources;
6 struct resource * resource;
7
8 const struct platform_device_id *id_entry;
9
10 /* arch specific additions */
11 struct pdev_archdata archdata;
12 };
当中的resource是platform驱动用到的资源，它是定义在<include/linux/ioport.h>中：
1 struct resource {
2 resource_size_t start;
3 resource_size_t end;
4 const char *name;
5 unsigned long flags;
6 struct resource *parent, *sibling, *child;
7 };platform_driver定义在<linux/platform_device.h>中：
1 struct platform_driver { 2 int (*probe)(struct platform_device *); 3 int (*remove)(struct platform_device *); 4 void (*shutdown)(struct platform_device *); 5 int (*suspend)(struct platform_device *, pm_message_t state); 6 int (*resume)(struct platform_device *); 7 struct device_driver driver; 8 const struct platform_device_id *id_table; 9 };系统中为platform总线定义了一个实例platform_bus_type，在<linux/platform_device.h>进行了声明：extern struct bus_type platform_bus_type;定义在drivers/base/platform.c中：1 struct bus_type platform_bus_type = { 2 .name = "platform", 3 .dev_attrs = platform_dev_attrs, 4 .match = platform_match, 5 .uevent = platform_uevent, 6 .pm = &platform_dev_pm_ops, 7 }; 8 EXPORT_SYMBOL_GPL(platform_bus_type);二、详细实现1、platform_match函数的实现（定义在drivers/base/platform.c中）：1 static const struct platform_device_id *platform_match_id( 2 const struct platform_device_id *id, 3 struct platform_device *pdev) 4 { 5 while (id->name[0]) { 6 if (strcmp(pdev->name, id->name) == 0) { 7 pdev->id_entry = id; 8 return id; 9 } 10 id++; 11 } 12 return NULL; 13 } 14 15 /** 16 * platform_match - bind platform device to platform driver. 17 * @dev: device. 18 * @drv: driver. 19 * 20 * Platform device IDs are assumed to be encoded like this: 21 * "<name><instance>", where <name> is a short description of the type of 22 * device, like "pci" or "floppy", and <instance> is the enumerated 23 * instance of the device, like '0' or '42'. Driver IDs are simply 24 * "<name>". So, extract the <name> from the platform_device structure, 25 * and compare it against the name of the driver. Return whether they match 26 * or not. 27 */ 28 static int platform_match(struct device *dev, struct device_driver *drv) 29 { 30 struct platform_device *pdev = to_platform_device(dev); 31 struct platform_driver *pdrv = to_platform_driver(drv); 32 33 /* Attempt an OF style match first */ 34 if (of_driver_match_device(dev, drv)) 35 return 1; 36 37 /* Then try to match against the id table */ 38 if (pdrv->id_table) 39 return platform_match_id(pdrv->id_table, pdev) != NULL; 40 41 /* fall-back to driver name match */ 42 return (strcmp(pdev->name, drv->name) == 0); 43 }是通过device的name和driver的name进行匹配的。
2、platform_device的定义和注冊
（platform_add_devices定义在drivers/base/platform.c中）1 /** 2 * platform_add_devices - add a numbers of platform devices 3 * @devs: array of platform devices to add 4 * @num: number of platform devices in array 5 */ 6 int platform_add_devices(struct platform_device **devs, int num) 7 { 8 int i, ret = 0; 9 10 for (i = 0; i < num; i++) { 11 ret = platform_device_register(devs[i]); 12 if (ret) { 13 while (--i >= 0) 14 platform_device_unregister(devs[i]); 15 break; 16 } 17 } 18 19 return ret; 20 } 21 EXPORT_SYMBOL_GPL(platform_add_devices);对于一个指定的板子来说，比方对于ldd6410的globalfifo驱动来说，要在mach-ldd6410.c中定义platform_device globalfifo_device,并将globalfifo_device放入ldd6410_devices数组中，代码例如以下所看到的。
3、platform_driver的操作
platform_driver的定义和注冊在对应驱动文件里实现，以下是《linux驱动开发具体解释》一书中globalfifo的样例的部分代码：
4、platform设备资源和数据
（1）、resource的定义（<linux/ioport.h>）
1 struct resource {
2 resource_size_t start;
3 resource_size_t end;
4 const char *name;
5 unsigned long flags;
6 struct resource *parent, *sibling, *child;
7 };
当flags是IORESOURCE_MEM时，start和end各自是资源的起始地址和结束地址；
当flags是IORESOURCE_IRQ时，start和end各自是资源的起始中断号和结束中断号；#define IORESOURCE_TYPE_BITS 0x00001f00 /* Resource type */
#define IORESOURCE_IO 0x00000100
#define IORESOURCE_MEM 0x00000200
#define IORESOURCE_IRQ 0x00000400
#define IORESOURCE_DMA 0x00000800
#define IORESOURCE_BUS 0x00001000对于同种类型的资源能够有两份或多份。（2）、获得资源
对resource的定义通常在板文件里，而驱动通过platform_get_resource获得资源（driver/base/platform.c）：
1 /** 2 * platform_get_resource - get a resource for a device 3 * @dev: platform device 4 * @type: resource type 5 * @num: resource index 6 */ 7 struct resource *platform_get_resource(struct platform_device *dev, 8 unsigned int type, unsigned int num) 9 { 10 int i; 11 12 for (i = 0; i < dev->num_resources; i++) { 13 struct resource *r = &dev->resource[i]; 14 15 if (type == resource_type(r) && num-- == 0) 16 return r; 17 } 18 return NULL; 19 } 20 EXPORT_SYMBOL_GPL(platform_get_resource);三、platform驱动的一个样例以linux-2.6.38内核的dm9000驱动为例说明平台驱动的定义和资源获取。1、platform_device和resource的定义（mach-mini6410.c）1 /* DM9000AEP 10/100 ethernet controller */ 2 /*dm9000的资源*/ 3 static struct resource mini6410_dm9k_resource[] = { 4 [0] = { 5 .start = S3C64XX_PA_XM0CSN1, 6 .end = S3C64XX_PA_XM0CSN1 + 1, 7 .flags = IORESOURCE_MEM 8 }, 9 [1] = { 10 .start = S3C64XX_PA_XM0CSN1 + 4, 11 .end = S3C64XX_PA_XM0CSN1 + 5, 12 .flags = IORESOURCE_MEM 13 }, 14 [2] = { 15 .start = S3C_EINT(7), 16 .end = S3C_EINT(7), 17 .flags = IORESOURCE_IRQ | IORESOURCE_IRQ_HIGHLEVEL 18 } 19 }; 20 /*dm9000_plat_data定义在<linux/dm9000.h>*/ 21 static struct dm9000_plat_data mini6410_dm9k_pdata = { 22 .flags = (DM9000_PLATF_16BITONLY | DM9000_PLATF_NO_EEPROM), 23 }; 24 25 static struct platform_device mini6410_device_eth = { 26 .name = "dm9000", 27 .id = -1, 28 .num_resources = ARRAY_SIZE(mini6410_dm9k_resource), 29 .resource = mini6410_dm9k_resource, 30 .dev = { 31 .platform_data = &mini6410_dm9k_pdata, 32 }, 33 }; 34 35 /*全部的设备存放在这个数组里，最后通过platform_add_devices进行注冊*/ 36 static struct platform_device *mini6410_devices[] __initdata = { 37 &mini6410_device_eth, 38 &s3c_device_hsmmc0, 39 &s3c_device_hsmmc1, 40 &s3c_device_ohci, 41 &s3c_device_nand, 42 &s3c_device_fb, 43 &mini6410_lcd_powerdev, 44 &s3c_device_adc, 45 &s3c_device_ts, 46 };2、platform_driver的定义和注冊（dm9000.c）1 static struct platform_driver dm9000_driver = { 2 .driver = { 3 .name = "dm9000", 4 .owner = THIS_MODULE, 5 .pm = &dm9000_drv_pm_ops, 6 }, 7 .probe = dm9000_probe, 8 .remove = __devexit_p(dm9000_drv_remove), 9 }; 10 11 static int __init 12 dm9000_init(void) 13 { 14 printk(KERN_INFO "%s Ethernet Driver, V%s\n", CARDNAME, DRV_VERSION); 15 16 return platform_driver_register(&dm9000_driver); 17 } 18 19 static void __exit 20 dm9000_cleanup(void) 21 { 22 platform_driver_unregister(&dm9000_driver); 23 }dm9000驱动获得定义在板文件里的platform_data的方法：struct platform_device *pdevstruct dm9000_plat_data *pdata = pdev->dev.platform_data;db->addr_res = platform_get_resource(pdev, IORESOURCE_MEM, 0);db->data_res = platform_get_resource(pdev, IORESOURCE_MEM, 1);db->irq_res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
platform_get_resource函数定义在drivers/base/platform.c中：1 /** 2 * platform_get_resource - get a resource for a device 3 * @dev: platform device 4 * @type: resource type 5 * @num: resource index 6 */ 7 struct resource *platform_get_resource(struct platform_device *dev, 8 unsigned int type, unsigned int num) 9 { 10 int i; 11 12 for (i = 0; i < dev->num_resources; i++) { 13 struct resource *r = &dev->resource[i]; 14 15 if (type == resource_type(r) && num-- == 0) 16 return r; 17 } 18 return NULL; 19 } 20 EXPORT_SYMBOL_GPL(platform_get_resource);
