本章重点讲解思想、思想、思想。
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”
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 1; /* Then try ACPI style match */ if (acpi_driver_match_device(dev, drv)) return 1; /* 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) == 0); }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。
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, 0); if (globalfifo_major) ret = register_chrdev_region(devno, 1, "globalfifo"); else { ret = alloc_chrdev_region(&devno, 0, 1, "globalfifo"); globalfifo_major = MAJOR(devno); } if (ret < 0) 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, 0); mutex_init(&globalfifo_devp->mutex); init_waitqueue_head(&globalfifo_devp->r_wait); init_waitqueue_head(&globalfifo_devp->w_wait); return 0; fail_malloc: unregister_chrdev_region(devno, 1); 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, 0), 1); return 0; } 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 = -1, };
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 */
稍后具体分析1个linux的驱动比较好。
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。
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。
转载于:https://www.cnblogs.com/liuwanpeng/p/7305338.html
