本章重点讲解思想、思想、思想。
12.1 linux驱动的软件架构
下述三种思想，在linux的spi、iic、usb等复杂驱动里广泛使用。后面几节分别对这些思想进行详细说明。
- 思想1：驱动与设备分离，linux采用总线、设备和驱动模型，驱动只管驱动，设备只管设备，总线负责匹配设备和驱动；驱动从标准途径拿到板级信息（设备信息，现在都已dts的形式存在），这样驱动就可以放之四海而皆准了，结构如下图。
说到“总线”，有很多种，如I2C、SPI等，linux还为没有硬件总线的设备提出一种虚拟总线，即platform总线，同时还有对应的platform设备和platform驱动。
为啥？ linux驱动要支持很多硬件，如果把设备信息写到驱动里，驱动会有非常多分支，一堆东西揉到一起，换成一锅粥，所以要把设备和驱动分开。
- 思想2：分层设计思想，file_opretations、IO模型等，是很多驱动共有的部分，linux提炼出一个中间层，把这些部分封装起来，供所有驱动使用。这就引出了软件分层的思想。
- 思想3：主机与外设分隔的思想。例如spi分为主机和外设，不同CPU有M种spi主机，同时不通外设也有N种，如果直接交叉支持，势必有M*N种组合，代码会非常复杂。需要在主机和外设中间插入一个标准API，把M和N分隔开，主机和外设都使用标准API与中间的分隔层接口，这样只需要实现M个主机和N个外设驱动即可，这种思想也叫“高内聚，低耦合”
12.2 platform设备驱动
12.2.1 platform总线、设备与驱动
- linux 2.6以后，采用总线、设备、驱动模型；
- platform的引入：有些设备本身依附一种总线，例如IIC、SPI、PCI、SPI等，很容易实现linux的总线/设备/驱动模型；但有些设备不依赖总线，例如SOC系统内部集成的独立外设控制器等，基于这种情况，linux发明了一种虚拟总线，即platform总线，对应的设备和驱动分别为platform_device和platform_driver。
- platform device不是针对linux的字符设备、块设备、网络设备的，是linux的一种附加手段。SOC内部集成的各控制器，例如IIC、RTC、LCD等一般都归纳为platform device。
- platform作为一种虚拟总线，与其他实体总线地位对等，例如SPI/IIC总线等，掌握了platform总线，其他总线也是类似的。
关键数据结构：
1. device
#include <linux/platform_device.h>
struct platform_device {
const char *name;
int id;
bool id_auto;
struct device dev; // linux/device.h里定义，总线match时，实际match的是dev，所有设备共性的部分
u32 num_resources; // 资源
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;
};
2.driver
#include <linux/platform_device.h>
// probe等函数由内核的platform机制实现了，驱动需要填充driver结构体
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); // 电源管理，基本不用了，有driver里的
int (*resume)(struct platform_device *); // 同上
struct device_driver driver; // 所有驱动共享的部分，match以后driver.probe执行，同时调用外层platform_driver的prove执行
const struct platform_device_id *id_table; // 一组ID表
bool prevent_deferred_probe;
}; // linux/device.h
/**
* struct device_driver - The basic device driver structure
* @name: Name of the device driver.
* @bus: The bus which the device of this driver belongs to.
* @owner: The module owner.
* @mod_name: Used for built-in modules.
* @suppress_bind_attrs: Disables bind/unbind via sysfs.
* @of_match_table: The open firmware table.
* @acpi_match_table: The ACPI match table.
* @probe: Called to query the existence of a specific device,
* whether this driver can work with it, and bind the driver
* to a specific device.
* @remove: Called when the device is removed from the system to
* unbind a device from this driver.
* @shutdown: Called at shut-down time to quiesce the device.
* @suspend: Called to put the device to sleep mode. Usually to a
* low power state.
* @resume: Called to bring a device from sleep mode.
* @groups: Default attributes that get created by the driver core
* automatically.
* @pm: Power management operations of the device which matched
* this driver.
* @p: Driver core's private data, no one other than the driver
* core can touch this.
*
* The device driver-model tracks all of the drivers known to the system.
* The main reason for this tracking is to enable the driver core to match
* up drivers with new devices. Once drivers are known objects within the
* system, however, a number of other things become possible. Device drivers
* can export information and configuration variables that are independent
* of any specific device.
*/
struct device_driver {
const char *name;
struct bus_type *bus; // 对应总线结构体指针 struct module *owner;
const char *mod_name; /* used for built-in modules */ bool suppress_bind_attrs; /* disables bind/unbind via sysfs */ const struct of_device_id *of_match_table;
const struct acpi_device_id *acpi_match_table; int (*probe) (struct device *dev); // 总线match完设备和驱动以后，这个函数会执行，
// 形参dev就是被match的设备信息！！！
int (*remove) (struct device *dev);
void (*shutdown) (struct device *dev);
int (*suspend) (struct device *dev, pm_message_t state);
int (*resume) (struct device *dev);
const struct attribute_group **groups; const struct dev_pm_ops *pm; struct driver_private *p;
};
3.总线
总线的类型为bus_type,内核直接为platform定义了一个总线实体
// drivers/base/platform.c，这些函数都是现成的，在platform机制里实现了。
struct bus_type platform_bus_type = {
.name = "platform",
.dev_groups = platform_dev_groups,
.match = platform_match, // 匹配函数，关键
.uevent = platform_uevent,
.pm = &platform_dev_pm_ops,
}; /**
* platform_match - bind platform device to platform driver.
* @dev: device.
* @drv: driver.
*
* Platform device IDs are assumed to be encoded like this:
* "<name><instance>", where <name> is a short description of the type of
* device, like "pci" or "floppy", and <instance> is the enumerated
* instance of the device, like '0' or '42'. Driver IDs are simply
* "<name>". So, extract the <name> from the platform_device structure,
* and compare it against the name of the driver. Return whether they match
* or not.
*/
static int platform_match(struct device *dev, struct device_driver *drv)
{
struct platform_device *pdev = to_platform_device(dev);
struct platform_driver *pdrv = to_platform_driver(drv); /* Attempt an OF style match first */ // 基于dts匹配优先级最高
if (of_driver_match_device(dev, drv))
return ; /* Then try ACPI style match */
if (acpi_driver_match_device(dev, drv))
return ; /* Then try to match against the id table */ // 基于platform device和platform driver的ID
if (pdrv->id_table)
return platform_match_id(pdrv->id_table, pdev) != NULL; /* fall-back to driver name match */ // 基于名字
return (strcmp(pdev->name, drv->name) == );
}
linux 2.6以及之前版本，platform device通常定义在板级bsp里，然后再add；而3.x以后，改为自动展开dts，形成若干device。
12.2.2 将globalmem作为platform设备
没法实验，只罗列代码。
static int globalfifo_probe(struct platform_device *pdev) // 完成原来globalmem_init的任务
{
int ret;
dev_t devno = MKDEV(globalfifo_major, ); if (globalfifo_major)
ret = register_chrdev_region(devno, , "globalfifo");
else {
ret = alloc_chrdev_region(&devno, , , "globalfifo");
globalfifo_major = MAJOR(devno);
}
if (ret < )
return ret; globalfifo_devp = devm_kzalloc(&pdev->dev, sizeof(*globalfifo_devp),GFP_KERNEL);
if (!globalfifo_devp) {
ret = -ENOMEM;
goto fail_malloc;
} globalfifo_setup_cdev(globalfifo_devp, ); mutex_init(&globalfifo_devp->mutex);
init_waitqueue_head(&globalfifo_devp->r_wait);
init_waitqueue_head(&globalfifo_devp->w_wait); return ; fail_malloc:
unregister_chrdev_region(devno, );
return ret;
} static int globalfifo_remove(struct platform_device *pdev) // 完成原来globalmem_exit的任务
{
cdev_del(&globalfifo_devp->cdev);
unregister_chrdev_region(MKDEV(globalfifo_major, ), ); return ;
} static struct platform_driver globalfifo_driver = {
.driver = {
.name = "globalfifo",
.owner = THIS_MODULE,
},
.probe = globalfifo_probe,
.remove = globalfifo_remove,
}; module_platform_driver(globalfifo_driver); // !!!注册platform驱动，/sys/bus/platform/drivers/globalmem,多出一个globalmem子目录
// 在板级bsp里(arch/arm/mach-xxx/mach-yyy.c,xxx为SOC名，yyy为board名)增加platform device，
// 系统初始化时添加到系统里，/sys/device/platform/globalmem,多出一个globalmem子目录，该目录中有driver符号链接,
// 指向/sys/bus/platform/drivers/globalmem
static struct platform_device globalfifo_device = {
.name = "globalfifo",
.id = -,
};
12.2.3 platform设备资源和数据
在platform_device结构体中，有resource结构体，表示该device的资源，start和end随flag的变化而表示不同的含义：
flag：
IORESOURCE_MEM，start和end表示platform device占据的开始开始地址和结束地址
- IORESOURCE_IRQ,start和end表示使用中断号的开始值和结束值，如果只有1个中断号，则开始值和结束值相同
resource在板级支持包或者dts里定义，dts的定义后续说明，板级支持包都淘汰了，不再说明。
/* 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;
}; /*
* IO resources have these defined flags.
*/
#define IORESOURCE_BITS 0x000000ff /* Bus-specific bits */ #define IORESOURCE_TYPE_BITS 0x00001f00 /* Resource type */
#define IORESOURCE_IO 0x00000100 /* PCI/ISA I/O ports */
#define IORESOURCE_MEM 0x00000200
#define IORESOURCE_REG 0x00000300 /* Register offsets */
#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 */ /* PnP IRQ specific bits (IORESOURCE_BITS) */
#define IORESOURCE_IRQ_HIGHEDGE (1<<0)
#define IORESOURCE_IRQ_LOWEDGE (1<<1)
#define IORESOURCE_IRQ_HIGHLEVEL (1<<2)
#define IORESOURCE_IRQ_LOWLEVEL (1<<3)
#define IORESOURCE_IRQ_SHAREABLE (1<<4)
#define IORESOURCE_IRQ_OPTIONAL (1<<5) /* PnP DMA specific bits (IORESOURCE_BITS) */
#define IORESOURCE_DMA_TYPE_MASK (3<<0)
#define IORESOURCE_DMA_8BIT (0<<0)
#define IORESOURCE_DMA_8AND16BIT (1<<0)
#define IORESOURCE_DMA_16BIT (2<<0) #define IORESOURCE_DMA_MASTER (1<<2)
#define IORESOURCE_DMA_BYTE (1<<3)
#define IORESOURCE_DMA_WORD (1<<4) #define IORESOURCE_DMA_SPEED_MASK (3<<6)
#define IORESOURCE_DMA_COMPATIBLE (0<<6)
#define IORESOURCE_DMA_TYPEA (1<<6)
#define IORESOURCE_DMA_TYPEB (2<<6)
#define IORESOURCE_DMA_TYPEF (3<<6) /* PnP memory I/O specific bits (IORESOURCE_BITS) */
#define IORESOURCE_MEM_WRITEABLE (1<<0) /* dup: IORESOURCE_READONLY */
#define IORESOURCE_MEM_CACHEABLE (1<<1) /* dup: IORESOURCE_CACHEABLE */
#define IORESOURCE_MEM_RANGELENGTH (1<<2) /* dup: IORESOURCE_RANGELENGTH */
#define IORESOURCE_MEM_TYPE_MASK (3<<3)
#define IORESOURCE_MEM_8BIT (0<<3)
#define IORESOURCE_MEM_16BIT (1<<3)
#define IORESOURCE_MEM_8AND16BIT (2<<3)
#define IORESOURCE_MEM_32BIT (3<<3)
#define IORESOURCE_MEM_SHADOWABLE (1<<5) /* dup: IORESOURCE_SHADOWABLE */
#define IORESOURCE_MEM_EXPANSIONROM (1<<6) /* PnP I/O specific bits (IORESOURCE_BITS) */
#define IORESOURCE_IO_16BIT_ADDR (1<<0)
#define IORESOURCE_IO_FIXED (1<<1) /* PCI ROM control bits (IORESOURCE_BITS) */
#define IORESOURCE_ROM_ENABLE (1<<0) /* ROM is enabled, same as PCI_ROM_ADDRESS_ENABLE */
#define IORESOURCE_ROM_SHADOW (1<<1) /* ROM is copy at C000:0 */
#define IORESOURCE_ROM_COPY (1<<2) /* ROM is alloc'd copy, resource field overlaid */
#define IORESOURCE_ROM_BIOS_COPY (1<<3) /* ROM is BIOS copy, resource field overlaid */ /* PCI control bits. Shares IORESOURCE_BITS with above PCI ROM. */
#define IORESOURCE_PCI_FIXED (1<<4) /* Do not move resource */
12.3 设备驱动的分层思想
稍后具体分析1个linux的驱动比较好。
12.4 主机驱动与外设驱动分离的设计思想
核心是定义好外设与主机之间的标准API，两边都使用标准API。具体分析一个驱动，便于理解。
12.5 总结
掌握思想，用这些思想去分析具体驱动，多读读驱动，慢慢就能理解这些思想了。