Android平台上PMEM的使用及Platform设备注册(二)
三、注册PMEM设备
这里我们除了描述PMEM设备，还将注册一个拥有memory空间和IRQ资源的示例设备example_device。
对于example_device，定义如下结构体：
static struct resource example_resources[] = {
[0] = {
.start = 0xC0000000,
.end = 0xC0020000,
.flags = IORESOURCE_MEM,
},
[1] = {
.start = 30,
.end = 30,
.flags = IORESOURCE_IRQ,
},
};
static struct platform_device example_device = {
.name = "example",
.id = 0,
.num_resources = ARRAY_SIZE(example_resources),
.resource = example_resources,
};
example_device设备拥有IORESOURCE_MEM和IORESOURCE_IRQ两种资源，其IORESOURCE_MEM的起始地址为0xC0000000，结束地址为0xC0020000，IORESOURCE_IRQ的中断号为30。
对于PMEM设备，我们先要介绍一下结构体android_pmem_platform_data。它被定义在文件/kernel/include/linux/android_pmem.h中。其定义为：
struct android_pmem_platform_data
{
const char* name;
/* starting physical address of memory region */
unsigned long start;
/* size of memory region */
unsigned long size;
/* set to indicate the region should not be managed with an allocator */
unsigned no_allocator;
/* set to indicate maps of this region should be cached, if a mix of
* cached and uncached is desired, set this and open the device with
* O_SYNC to get an uncached region */
unsigned cached;
/* The MSM7k has bits to enable a write buffer in the bus controller*/
unsigned buffered;
};
我们为PMEM设备定义如下结构体：
static struct android_pmem_platform_data android_pmem0_pdata = {
.name = "pmem0",
.start = PMEM_0_BASE,
.size = PMEM_0_SIZE,
.no_allocator = 0,
.cached = 1,
};
static struct android_pmem_platform_data android_pmem1_pdata = {
.name = "pmem1",
.start = PMEM_1_BASE,
.size = PMEM_1_SIZE,
.no_allocator = 0,
.cached = 1,
};
struct platform_device android_pmem0_device = {
.name = "android_pmem",
.id = 0,
.dev = { .platform_data = &android_pmem0_pdata },
};
struct platform_device android_pmem1_device = {
.name = "android_pmem",
.id = 1,
.dev = { .platform_data = &android_pmem1_pdata },
};
然后将这几个设备结构体放置到一个platform_device的数组中，
static struct platform_device *devices[] __initdata = {
&example_device,
&android_pmem0_device,
&android_pmem1_device,
};
最后通过调用函数platform_add_devices()向系统中添加这些设备。
static void __init androidphone_init(void)
{
……
platform_add_devices(devices, ARRAY_SIZE(devices));
……
}
函数platform_add_devices()内部调用platform_device_register( )进行设备注册。要注意的是，这里的platform_device设备的注册过程必须在相应设备驱动加载之前被调用，即执行platform_driver_register()之前，原因是驱动注册时需要匹配内核中所有已注册的设备名。
函数platform_add_devices()定义在文件/kernel/driver/base/platform.c中，
/**
* platform_add_devices - add a numbers of platform devices
* @devs: array of platform devices to add
* @num: number of platform devices in array
*/
int platform_add_devices(struct platform_device **devs, int num)
{
int i, ret = 0;
for (i = 0; i < num; i++) {
ret = platform_device_register(devs[i]);
if (ret) {
while (--i >= 0)
platform_device_unregister(devs[i]);
break;
}
}
return ret;
}
EXPORT_SYMBOL_GPL(platform_add_devices);
最后，需要说明的结构体是platform_driver，它的原型定义，在
/kernel/include/linux/platform_device.h中，代码如下：
| struct platform_driver { int (*probe)(struct platform_device *); int (*remove)(struct platform_device *); void (*shutdown)(struct platform_device *); int (*suspend)(struct platform_device *, pm_message_t state); int (*resume)(struct platform_device *); struct device_driver driver; struct platform_device_id *id_table; }; |
内核提供的platform_driver结构体的注册函数为platform_driver_register()，其原型定义在/kernel/driver/base/platform.c文件中，具体实现代码如下：
/**
* platform_driver_register
* @drv: platform driver structure
*/
int platform_driver_register(struct platform_driver *drv)
{
drv->driver.bus = &platform_bus_type;
if (drv->probe)
drv->driver.probe = platform_drv_probe;
if (drv->remove)
drv->driver.remove = platform_drv_remove;
if (drv->shutdown)
drv->driver.shutdown = platform_drv_shutdown;
return driver_register(&drv->driver);
}
EXPORT_SYMBOL_GPL(platform_driver_register);
如果想深入了解Platform机制，可以参考下面的文章：
Linux Platform驱动程序框架解析
http://www.linuxidc.com/Linux/2011-01/31291.htm
Linux内核驱动的的platform机制
http://intq.blog.163.com/blog/static/671231452010124112546491/
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Date：2011/5/14
Blog：http://blog.csdn.net/wxzking
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