linux platform总线的相关总结

1 概述
1.1 简介
从Linux2.6起，引入了一套新的驱动管理和注册机制，包括三部分：Platform_bus，Platform_device和Platform_driver。Linux中大部分的设备驱动，都可以使用这套机制，设备用platform_device表示，驱动用platform_driver表示。

Platform bus属于内核的一部分，驱动程序可以不用关注，详细信息可以参考drivers/base/platform.c。

Linux platform driver机制和传统的device_driver机制相比，一个十分明显的优势在于platform机制将本身的资源注册进内核，由内核统一管理，在驱动程序中使用这些资源时通过platform_device提供的标准接口进行申请并使用。这样提高了驱动和资源管理的独立性，并且拥有较好的可移植性和安全性。

对于硬件来说，资源可以是中断、IO地址空间。

See

struct platform_device {    const char  * name;    int     id;    struct device   dev;    u32     num_resources;    struct resource * resource;    const struct platform_device_id *id_entry;    /* MFD cell pointer */    struct mfd_cell *mfd_cell;    /* arch specific additions */    struct pdev_archdata    archdata;};

3.1.2 Struct resource

struct resource {    resource_size_t start;    resource_size_t end;    const char *name;    unsigned long flags;    struct resource *parent, *sibling, *child;};    资源的类型    /* * IO resources have these defined flags. */#define IORESOURCE_BITS     0x000000ff  /* Bus-specific bits */#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#define IORESOURCE_PREFETCH 0x00002000  /* No side effects */#define IORESOURCE_READONLY 0x00004000#define IORESOURCE_CACHEABLE    0x00008000#define IORESOURCE_RANGELENGTH  0x00010000#define IORESOURCE_SHADOWABLE   0x00020000#define IORESOURCE_SIZEALIGN    0x00040000  /* size indicates alignment */#define IORESOURCE_STARTALIGN   0x00080000  /* start field is alignment */#define IORESOURCE_MEM_64   0x00100000#define IORESOURCE_WINDOW   0x00200000  /* forwarded by bridge */#define IORESOURCE_MUXED    0x00400000  /* Resource is software muxed */#define IORESOURCE_EXCLUSIVE    0x08000000  /* Userland may not map this resource */#define IORESOURCE_DISABLED 0x10000000#define IORESOURCE_UNSET    0x20000000#define IORESOURCE_AUTO     0x40000000#define IORESOURCE_BUSY     0x80000000  /* Driver has marked this resource busy */

常用的有：
IORESOURCE_MEM
IORESOURCE_IRQ

3.1.3 主要接口：

int platform_driver_register(struct platform_driver *drv);

1.1 设备枚举
在调用platform_device_register注册设备驱动的过程中调用注册的probe函数。
详细说明如下：
As a rule, platform specific (and often board-specific) setup code will register platform devices:
int platform_device_register(struct platform_device *pdev);
int platform_add_devices(struct platform_device **pdevs, int ndev);

The general rule is to register only those devices that actually exist,
but in some cases extra devices might be registered. For example, a kernel
might be configured to work with an external network adapter that might not
be populated on all boards, or likewise to work with an integrated controller
that some boards might not hook up to any peripherals.

In some cases, boot firmware will export tables describing the devices
that are populated on a given board. Without such tables, often the
only way for system setup code to set up the correct devices is to build
a kernel for a specific target board. Such board-specific kernels are
common with embedded and custom systems development.

In many cases, the memory and IRQ resources associated with the platform
device are not enough to let the device’s driver work. Board setup code
will often provide additional information using the device’s platform_data
field to hold additional information.

Embedded systems frequently need one or more clocks for platform devices,
which are normally kept off until they’re actively needed (to save power).
System setup also associates those clocks with the device, so that that
calls to clk_get(&pdev->dev, clock_name) return them as needed.