platform_device_系列函數，實際上是注冊了一個叫platform的虛擬總線。使用約定是如果一個不屬于任何總線的設備，例如藍牙，串口等設備，都需要掛在這個虛擬總線上。

driver/base/platform.c

//platform設備聲明
struct device platform_bus = {
??? .bus_id??????? = "platform",
};
EXPORT_SYMBOL_GPL(platform_bus);

//platform總線設備聲明
struct bus_type platform_bus_type = {
??? .name??????? = "platform",
??? .dev_attrs??? = platform_dev_attrs,
??? .match??????? = platform_match,
??? .uevent??????? = platform_uevent,
??? .suspend??? = platform_suspend,
??? .suspend_late??? = platform_suspend_late,
??? .resume_early??? = platform_resume_early,
??? .resume??????? = platform_resume,
};
EXPORT_SYMBOL_GPL(platform_bus_type);

int __init platform_bus_init(void)
{
??? int error;

??? error = device_register(&platform_bus);//注冊了"platform"的設備
??? if (error)
??????? return error;
??? error = bus_register(&platform_bus_type);//注冊了叫"platform"的總線
??? if (error)
??????? device_unregister(&platform_bus);
??? return error;
}


//這里在platform總線上掛設備
int platform_device_add(struct platform_device *pdev)
{
??? int i, ret = 0;

??? if (!pdev)
??????? return -EINVAL;

??? if (!pdev->dev.parent)
??????? pdev->dev.parent = &platform_bus;//父設備設置為platform_bus

??? pdev->dev.bus = &platform_bus_type;//設置掛在platform總線上

??? if (pdev->id != -1)
??????? snprintf(pdev->dev.bus_id, BUS_ID_SIZE, "%s.%d", pdev->name,
???????????? pdev->id);
??? else
??????? strlcpy(pdev->dev.bus_id, pdev->name, BUS_ID_SIZE);

??? for (i = 0; i < pdev->num_resources; i++) {
??????? struct resource *p, *r = &pdev->resource[i];

??????? if (r->name == NULL)
??????????? r->name = pdev->dev.bus_id;

??????? p = r->parent;
??????? if (!p) {
??????????? if (r->flags & IORESOURCE_MEM)
??????????????? p = &iomem_resource;
??????????? else if (r->flags & IORESOURCE_IO)
??????????????? p = &ioport_resource;
??????? }

??????? if (p && insert_resource(p, r)) {
??????????? printk(KERN_ERR
?????????????????? "%s: failed to claim resource %d\n",
?????????????????? pdev->dev.bus_id, i);
??????????? ret = -EBUSY;
??????????? goto failed;
??????? }
??? }

??? pr_debug("Registering platform device '%s'. Parent at %s\n",
???????? pdev->dev.bus_id, pdev->dev.parent->bus_id);

??? ret = device_add(&pdev->dev);
??? if (ret == 0)
??????? return ret;

failed:
??? while (--i >= 0)
??????? if (pdev->resource[i].flags & (IORESOURCE_MEM|IORESOURCE_IO))
??????????? release_resource(&pdev->resource[i]);
??? return ret;
}
EXPORT_SYMBOL_GPL(platform_device_add);


//常用的platform_device_register，內部調用了platform_device_add，將設備掛在了platform總線上
/**
* platform_device_register - add a platform-level device
* @pdev: platform device we're adding
*/
int platform_device_register(struct platform_device *pdev)
{
??? device_initialize(&pdev->dev);
??? return platform_device_add(pdev);
}
EXPORT_SYMBOL_GPL(platform_device_register);

要用注冊一個platform驅動的步驟：
1，注冊設備platform_device_register
2，注冊驅動platform_driver_register
注冊時候的兩個名字必須一樣，才能match上，才能work,例如：
struct platform_device pxa3xx_device_nand = {
??? .name??????? = "pxa3xx-nand",
??? .id??????? = -1,
??? .dev??????? = {
??????? .dma_mask = &pxa3xx_nand_dma_mask,
??????? .coherent_dma_mask = DMA_BIT_MASK(32),
??? },
??? .resource??? = pxa3xx_resource_nand,
??? .num_resources??? = ARRAY_SIZE(pxa3xx_resource_nand),
};

static struct platform_driver pxa3xx_nand_driver = {
??? .driver = {
??????? .name??? = "pxa3xx-nand",
??? },
??? .probe??????? = pxa3xx_nand_probe,
??? .remove??????? = pxa3xx_nand_remove,
#ifdef CONFIG_PM
??? .suspend??? = pxa3xx_nand_suspend,
??? .resume??????? = pxa3xx_nand_resume,
#endif
};

而且device注冊的時候，可以給driver傳參數

struct device {
??? struct klist??????? klist_children;
??? struct klist_node??? knode_parent;??? /* node in sibling list */
??? struct klist_node??? knode_driver;
??? struct klist_node??? knode_bus;
??? struct device??????? *parent;

??? struct kobject kobj;
??? char??? bus_id[BUS_ID_SIZE];??? /* position on parent bus */
??? struct device_type??? *type;
??? unsigned??????? is_registered:1;
??? unsigned??????? uevent_suppress:1;

??? struct semaphore??? sem;??? /* semaphore to synchronize calls to
???????????????????? * its driver.
???????????????????? */

??? struct bus_type??? *bus;??????? /* type of bus device is on */
??? struct device_driver *driver;??? /* which driver has allocated this
?????????????????????? device */
??? void??????? *driver_data;??? /* data private to the driver */
??? void??????? *platform_data;??? /* Platform specific data, device
?????????????????????? core doesn't touch it */
??? struct dev_pm_info??? power;

#ifdef CONFIG_NUMA
??? int??????? numa_node;??? /* NUMA node this device is close to */
#endif
??? u64??????? *dma_mask;??? /* dma mask (if dma'able device) */
??? u64??????? coherent_dma_mask;/* Like dma_mask, but for
???????????????????????? alloc_coherent mappings as
???????????????????????? not all hardware supports
???????????????????????? 64 bit addresses for consistent
???????????????????????? allocations such descriptors. */

??? struct device_dma_parameters *dma_parms;

??? struct list_head??? dma_pools;??? /* dma pools (if dma'ble) */

??? struct dma_coherent_mem??? *dma_mem; /* internal for coherent mem
???????????????????????? override */
??? /* arch specific additions */
??? struct dev_archdata??? archdata;

??? spinlock_t??????? devres_lock;
??? struct list_head??? devres_head;

??? /* class_device migration path */
??? struct list_head??? node;
??? struct class??????? *class;
??? dev_t??????????? devt;??? /* dev_t, creates the sysfs "dev" */
??? struct attribute_group??? **groups;??? /* optional groups */

??? void??? (*release)(struct device *dev);
};
傳參數都是通過platform_data傳，所以定義為void *
??? void??????? *platform_data;??? /* Platform specific data, device




static struct pxa3xx_nand_platform_data XXX_nand_info = {
??? .parts??????????? = android_256m_v75_partitions,
??? .nr_parts??????? = ARRAY_SIZE(android_256m_v75_partitions),
};

static void __init XXX_init_nand(void)
{
??? pxa3xx_device_nand.dev.platform_data = &XXX_nand_info;
??? platform_device_register(&pxa3xx_device_nand);
}




static int __init pxa3xx_nand_probe(struct platform_device *pdev)
{
??? struct pxa3xx_nand_platform_data *pdata;
??? struct nand_chip *this;
??? struct pxa3xx_nand_info *info;
??? struct resource *res;
??? struct clk *clk = NULL, *smc_clk = NULL;
??? int status = -1;
??? struct mtd_partition *parts;
??? unsigned int data_buf_len;
#ifdef CONFIG_MTD_NAND_PXA3xx_DMA
??? unsigned int buf_len;
#endif
??? int i, ret = 0;
#ifdef CONFIG_MTD_PARTITIONS
??? int err;
#endif

??? pdata = pdev->dev.platform_data;
....
....
....
}

下面解釋一下pxa_register_device函數
??? pxa_set_ohci_info(&XXX_ohci_info);

void __init pxa_set_ohci_info(struct pxaohci_platform_data *info)
{
??? pxa_register_device(&pxa27x_device_ohci, info);
}

void __init pxa_register_device(struct platform_device *dev, void *data)
{
??? int ret;

??? dev->dev.platform_data = data;

??? ret = platform_device_register(dev);
??? if (ret)
??????? dev_err(&dev->dev, "unable to register device: %d\n", ret);
}

其實上，也就是給driver傳參數，通過dev.platform_data。

到這里，platform_device系列函數，基本算通了，系列函數還有一堆設置的函數，和device_register同級別的那些功能函數，用法基本差不多，只不過都將設備掛在了platform總線上。

?

?

platform_device_register向系統注冊設備

platform_driver_register向系統注冊驅動，過程中在系統尋找注冊的設備（根據.name)，找到后運行.probe進行初始化。

?

?

***************************************************************

device_register()和platform_device_register()的區別(轉載)??


首先看device和platform_device區別
由struct platform_device {
const char * name; //NOTE:此處設備的命名應和相應驅動程序命名一致
u32 id;????????????//以實現driver binding
struct device dev;
u32 num_resources;
struct resource * resource;
};
可知：platform_device由device派生而來

內核中關于Platform devices的注釋
Platform devices
~~~~~~~~~~~~~~~~
Platform devices are devices that typically appear as autonomous
entities in the system. This includes legacy port-based devices and
host bridges to peripheral buses, and most controllers integrated
into system-on-chip platforms. What they usually have in common
is direct addressing from a CPU bus. Rarely, a platform_device will
be connected through a segment of some other kind of bus; but its
registers will still be directly addressable.

Platform devices are given a name, used in driver binding, and a
list of resources such as addresses and IRQs.
個人理解：Platform devices是相對獨立的設備，擁有各自獨自的資源（addresses and IRQs）

一個Platform devices實例：
static struct platform_device *smdk2410_devices[] __initdata = {
&s3c_device_usb, //片上的各個設備
&s3c_device_lcd, //下面以s3c_device_lcd為例
&s3c_device_wdt,
&s3c_device_i2c,
&s3c_device_iis,
};

/* LCD Controller */
static struct resource s3c_lcd_resource[] = { //LCD的兩個資源
[0] = {
.start = S3C2410_PA_LCD,
.end = S3C2410_PA_LCD + S3C2410_SZ_LCD,
.flags = IORESOURCE_MEM,
},
[1] = {
.start = IRQ_LCD,
.end = IRQ_LCD,
.flags = IORESOURCE_IRQ,
}

};

struct platform_device s3c_device_lcd = {//s3c_device_lcd設備
.name = "s3c2410-lcd",
.id = -1,
.num_resources = ARRAY_SIZE(s3c_lcd_resource),
.resource = s3c_lcd_resource,
.dev = { //device實例
.dma_mask = &s3c_device_lcd_dmamask,
.coherent_dma_mask = 0xffffffffUL
}
};

s3c_device_lcd的resource中硬件地址:

#define S3C2410_LCDREG(x) ((x) + S3C2410_VA_LCD)

/* LCD control registers */
#define S3C2410_LCDCON1 S3C2410_LCDREG(0x00)
#define S3C2410_LCDCON2 S3C2410_LCDREG(0x04)
#define S3C2410_LCDCON3 S3C2410_LCDREG(0x08)
#define S3C2410_LCDCON4 S3C2410_LCDREG(0x0C)
#define S3C2410_LCDCON5 S3C2410_LCDREG(0x10)

#define S3C2410_LCDCON1_CLKVAL(x) ((x) << 8)
#define S3C2410_LCDCON1_MMODE (1<<7)
#define S3C2410_LCDCON1_DSCAN4 (0<<5)
#define S3C2410_LCDCON1_STN4 (1<<5)
#define S3C2410_LCDCON1_STN8 (2<<5)
#define S3C2410_LCDCON1_TFT (3<<5)
－－－－－－－－－－－－－－－－－－－－－－－－－－
#define S3C2410_ADDR(x) (0xF0000000 + (x))

/* LCD controller */
#define S3C2410_VA_LCD S3C2410_ADDR(0x00600000)
#define S3C2410_PA_LCD (0x4D000000)
#define S3C2410_SZ_LCD SZ_1M

再分析device_register()和platform_device_register()的實現代碼：

device_register()－－－－－－－－－－－－－－－－－－－－－－－－

/**
* device_register - register a device with the system.
* @dev: pointer to the device structure
*
* This happens in two clean steps - initialize the device
* and add it to the system. The two steps can be called
* separately, but this is the easiest and most common.
* I.e. you should only call the two helpers separately if
* have a clearly defined need to use and refcount the device
* before it is added to the hierarchy.
*/

int device_register(struct device *dev)
{
device_initialize(dev); //初始化設備結構
return device_add(dev); //添加設備到設備層
}

platform_device_register()－－－－－－－－－－－－－－－－－－－－
/**
* platform_device_register - add a platform-level device
* @pdev: platform device we're adding
*
*/
int platform_device_register(struct platform_device * pdev)
{
device_initialize(&pdev->dev); //初始化設備結構
return platform_device_add(pdev); //添加一個片上的設備到設備層
}
由以上函數可知：device_register()和platform_device_register()都會首先初始化設備
區別在于第二步：其實platform_device_add()包括device_add(),只不過要先注冊resources


platform_device_add()－－－－－－－－－－－－－－－－－－－－－－
/**
* platform_device_add - add a platform device to device hierarchy
* @pdev: platform device we're adding
*
* This is part 2 of platform_device_register(), though may be called
* separately _iff_ pdev was allocated by platform_device_alloc().
*/
int platform_device_add(struct platform_device *pdev)
{
int i, ret = 0;
if (!pdev)
return -EINVAL;
if (!pdev->dev.parent)
pdev->dev.parent = &platform_bus;
pdev->dev.bus = &platform_bus_type;

/*＋＋＋＋＋＋＋＋＋＋＋＋＋＋
The platform_device.dev.bus_id is the canonical name for the devices.
It's built from two components:

* platform_device.name ... which is also used to for driver matching.
* platform_device.id ... the device instance number, or else "-1"
to indicate there's only one.

These are concatenated, so name/id "serial"/0 indicates bus_id "serial.0", and
"serial/3" indicates bus_id "serial.3"; both would use the platform_driver
named "serial". While "my_rtc"/-1 would be bus_id "my_rtc" (no instance id)
and use the platform_driver called "my_rtc".
＋＋＋＋＋＋＋＋＋＋＋＋＋＋*/

if (pdev->id != -1)
snprintf(pdev->dev.bus_id, BUS_ID_SIZE, "%s.%u", pdev->name, pdev->id);
else //"-1" indicate there's only one
strlcpy(pdev->dev.bus_id, pdev->name, BUS_ID_SIZE);
for (i = 0; i < pdev->num_resources; i++) { //遍歷設備資源個數，如LCD的兩個資源：控制器和IRQ
struct resource *p, *r = &pdev->resource[i];
if (r->name == NULL)
r->name = pdev->dev.bus_id;
p = r->parent;
if (!p) { //resources分為兩種IORESOURCE_MEM和IORESOURCE_IO
??????????//CPU對外設IO端口物理地址的編址方式有兩種：I/O映射方式和內存映射方式
if (r->flags & IORESOURCE_MEM)
p = &iomem_resource;
else if (r->flags & IORESOURCE_IO)
p = &ioport_resource;
}

if (p && insert_resource(p, r)) {
printk(KERN_ERR
"%s: failed to claim resource %d/n",
pdev->dev.bus_id, i);
ret = -EBUSY;
goto failed;
}
}
pr_debug("Registering platform device '%s'. Parent at %s/n",
pdev->dev.bus_id, pdev->dev.parent->bus_id);
ret = device_add(&pdev->dev);
if (ret == 0)
return ret;
failed:
while (--i >= 0)
if (pdev->resource[i].flags & (IORESOURCE_MEM|IORESOURCE_IO))
release_resource(&pdev->resource[i]);
return ret;
}

相關參考＋＋＋＋＋＋＋＋＋＋＋＋＋＋＋＋＋＋＋＋＋＋＋
device_initialize()－－－－－－－－－－－－－－－－－－
/** </drivers/base/core.c>
* device_initialize - init device structure.
* @dev: device.
*
* This prepares the device for use by other layers,
* including adding it to the device hierarchy.
* It is the first half of device_register(), if called by
* that, though it can also be called separately, so one
* may use @dev's fields (e.g. the refcount).
*/

void device_initialize(struct device *dev)
{
kobj_set_kset_s(dev, devices_subsys);
kobject_init(&dev->kobj);
klist_init(&dev->klist_children, klist_children_get,
klist_children_put);
INIT_LIST_HEAD(&dev->dma_pools);
INIT_LIST_HEAD(&dev->node);
init_MUTEX(&dev->sem);
spin_lock_init(&dev->devres_lock);
INIT_LIST_HEAD(&dev->devres_head);
device_init_wakeup(dev, 0);
set_dev_node(dev, -1);
}
device_add(struct device *dev)－－－－－－－－－－－－－
/**
* device_add - add device to device hierarchy.
* @dev: device.
*
* This is part 2 of device_register(), though may be called
* separately _iff_ device_initialize() has been called separately.
*
* This adds it to the kobject hierarchy via kobject_add(), adds it
* to the global and sibling lists for the device, then
* adds it to the other relevant subsystems of the driver model.
*/
結構體resource－－－－－－－－－－－－－－－－－－－－－－
/* < /include/linux/ioport.h>
* Resources are tree-like, allowing
* nesting etc..
*/
struct resource {
resource_size_t start;
resource_size_t end;
const char *name;
unsigned long flags;
struct resource *parent, *sibling, *child;
};
－－－－－－－－－－－－－－－－－－－－－－－－－－－

原文地址:http://blog.chinaunix.net/u1/58968/showart_467998.html ,

在8250.c(driver/serial/8250.c)的初始化函數serial8250_init（）中，給出了一個很簡單的例子

static struct platform_device *serial8250_isa_devs;

......

//create a platform_device

serial8250_isa_devs = platform_device_alloc("serial8250",PLAT8250_DEV_LEGACY);??????????????

??platform_device_add(serial8250_isa_devs);?? //add the platform_device to system

platform_driver_register(&serial8250_isa_driver);//then register the platform_driver????????

還有另外一個比較類似的比較，就是driver_register和platform_driver_register的比較
????platform_driver_register(&xx_driver) 會向系統注冊xx_driver這個驅動程序，這個函數會根據 xx_driver中的.name內容，搜索系統注冊的device中有沒有這個platform_device,如果有，就會執行 platform_driver(也就是xx_driver的類型)中的.probe函數。

?

????? 對只需要初始化運行一次的函數都加上__init屬性，__init 宏告訴編譯器如果這個模塊被編譯到內核則把這個函數放到（.init.text）段，module_exit的參數卸載時同__init類似，如果驅動被編譯進內核，則__exit宏會忽略清理函數，因為編譯進內核的模塊不需要做清理工作，顯然__init和__exit對動態加載的模塊是無效的，只支持完全編譯進內核。

?

總結

以上是生活随笔為你收集整理的platform_device_系列函数及其设备注册的作用的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。