platform总线

1、平台总线模型

平台总线模型是Linux系统虚拟出来的总线，而I2C、SPI等物理总线是真实存在的。
平台总线模型将一个驱动分成两个部分，分别是device.c和driver.c，分别用来描述硬件信息和控制硬件。
平台总线通过字符串比较，将name相同的device.c和driver.c匹配到一起来控制硬件。
在这里插入图片描述

平台总线模型的优点：

减少编写重复代码，提高效率
提高代码的利用率

2、platform device

//\Linux-4.9.88\include\linux\platform_device.h
struct platform_device {
	const char	*name;//设备名
	int		id; //设备ID号
	bool		id_auto;
	struct device	dev; //包含一个具体的device结构体
	u32		num_resources; //资源的数量
	struct resource	*resource; //用来保存硬件资源的结构体    io资源，中断资源，内存资源

	const struct platform_device_id	*id_entry; //平台设备的id
	char *driver_override; /* Driver name to force a match */

	/* MFD cell pointer */
	struct mfd_cell *mfd_cell; //用户多功能卡，多功能设备的实现

	/* arch specific additions */
	struct pdev_archdata	archdata;
};
extern int platform_device_register(struct platform_device *); //注册平台总线设备
extern void platform_device_unregister(struct platform_device *);//删除平台总线设备

2.1、struct device

struct device {
	struct device		*parent;

	struct device_private	*p;

	struct kobject kobj;
	const char		*init_name; /* initial name of the device */
	const struct device_type *type;

	struct mutex		mutex;	/* mutex 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		*platform_data;	/* Platform specific data, device
					   core doesn't touch it */
	void		*driver_data;	/* Driver data, set and get with
					   dev_set/get_drvdata */
	struct dev_links_info	links;
	struct dev_pm_info	power;
	struct dev_pm_domain	*pm_domain;

#ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
	struct irq_domain	*msi_domain;
#endif
#ifdef CONFIG_PINCTRL
	struct dev_pin_info	*pins;
#endif
#ifdef CONFIG_GENERIC_MSI_IRQ
	struct list_head	msi_list;
#endif

#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. */
	unsigned long	dma_pfn_offset;

	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 */
#ifdef CONFIG_DMA_CMA
	struct cma *cma_area;		/* contiguous memory area for dma
					   allocations */
#endif
	/* arch specific additions */
	struct dev_archdata	archdata;

	struct device_node	*of_node; /* associated device tree node */
	struct fwnode_handle	*fwnode; /* firmware device node */

	dev_t			devt;	/* dev_t, creates the sysfs "dev" */
	u32			id;	/* device instance */

	spinlock_t		devres_lock;
	struct list_head	devres_head;

	struct klist_node	knode_class;
	struct class		*class;
	const struct attribute_group **groups;	/* optional groups */

	void	(*release)(struct device *dev);
	struct iommu_group	*iommu_group;
	struct iommu_fwspec	*iommu_fwspec;

	bool			offline_disabled:1;
	bool			offline:1;
};

3、platform driver

这个结构体包含了平台驱动需要实现的相关函数操作

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; //内嵌了一个设备驱动结构体
	/*平台设备ID，这与platform_device中的struct platform_device_id *id_entry是相同的
     主要是完成总线的匹配操作，platform总线的匹配操作第一匹配要素就是该元素。而不再是简单的name选项*/
	const struct platform_device_id *id_table;
	bool prevent_deferred_probe;
};

3.1、 struct device_driver

struct device_driver {
	const char		*name;
	struct bus_type		*bus;

	struct module		*owner;
	const char		*mod_name;	/* used for built-in modules */

	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */
	enum probe_type probe_type;

	const struct of_device_id	*of_match_table;
	const struct acpi_device_id	*acpi_match_table;

	int (*probe) (struct device *dev);
	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;
};

4、实验demo

4.1 platform_device.c

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <linux/platform_device.h>

//static struct resource  * res;

static void platform_dev_release(struct device *dev)
{
    printk("this is a test for platform_device\n");
} 

static struct resource platform_dev_resource[] = {

};

struct platform_device platform_dev_test = {
    .name = "100ask_test",
    .num_resources = ARRAY_SIZE(platform_dev_resource),
    .id = -1,
    .resource = platform_dev_resource,
    .dev = {
        .release = platform_dev_release,
    },
};

static int __init platform_dev_test_init(void)
{
    int err;
    
    err = platform_device_register(&platform_dev_test);   
    
    return 0;
}

static void __exit platform_dev_test_exit(void)
{
    platform_device_unregister(&platform_dev_test);

}

module_init(platform_dev_test_init);
module_exit(platform_dev_test_exit);

MODULE_LICENSE("GPL");

4.2 platform_driver.c

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <linux/platform_device.h>



static int platform_drv_probe(struct platform_device *pdev)
{
    printk("this is a test for platform_drv\n");
    return 0;
    
}

static int platform_drv_remove(struct platform_device *pdev)
{
    printk("this is in platform_drv_remove\n");
    return 0;
}


static struct platform_driver platform_drv_test = {
    .probe      = platform_drv_probe,
    .remove     = platform_drv_remove,
    .driver     = {
        .name   = "100ask_test",
    },
};

static int __init platform_drv_test_init(void)
{
    int err;
    
    err = platform_driver_register(&platform_drv_test); 
    return 0;
}

static void __exit platform_drv_test_exit(void)
{
    platform_driver_unregister(&platform_drv_test);
}

module_init(platform_drv_test_init);
module_exit(platform_drv_test_exit);

MODULE_LICENSE("GPL");

4.3 Makefile


# 1. 使用不同的开发板内核时, 一定要修改KERN_DIR
# 2. KERN_DIR中的内核要事先配置、编译, 为了能编译内核, 要先设置下列环境变量:
# 2.1 ARCH,          比如: export ARCH=arm64
# 2.2 CROSS_COMPILE, 比如: export CROSS_COMPILE=aarch64-linux-gnu-
# 2.3 PATH,          比如: export PATH=$PATH:/home/book/100ask_roc-rk3399-pc/ToolChain-6.3.1/gcc-linaro-6.3.1-2017.05-x86_64_aarch64-linux-gnu/bin 
# 注意: 不同的开发板不同的编译器上述3个环境变量不一定相同,
#       请参考各开发板的高级用户使用手册

KERN_DIR = /home/johan/share/linux_bsp/100ask_imx6ull-sdk/Linux-4.9.88

all:
	make -C $(KERN_DIR) M=`pwd` modules 
	

clean:
	make -C $(KERN_DIR) M=`pwd` modules clean


# 参考内核源码drivers/char/ipmi/Makefile
# 要想把a.c, b.c编译成ab.ko, 可以这样指定:
# ab-y := a.o b.o
# obj-m += ab.o

#编译成ko
platform_dev-y := platform_device.o
platform_drv-y := platform_driver.o
obj-m	+= platform_dev.o
obj-m	+= platform_drv.o