驱动移植 iTOP-4412 gpio-leds

阅读量

基于 iTOP-4412 POP 1G 精英板 + linux-4.19.323，学习一下 gpio-leds 驱动。


设备树（DTS）配置

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// arch/arm/boot/dts/exynos4412-itop-pop1g-elite.dts

leds {
    compatible = "gpio-leds";

    led2 {
        label = "red:system";
        gpios = <&gpx1 0 GPIO_ACTIVE_HIGH>;
        default-state = "off";
        linux,default-trigger = "heartbeat";
    };

    led3 {
        label = "red:user";
        gpios = <&gpk1 1 GPIO_ACTIVE_HIGH>;
        default-state = "off";
    };
};
  • leds节点描述了LED相关的硬件资源。
  • compatible = "gpio-leds"：这是最关键的特性，确保该节点由 drivers/leds/leds-gpio.c驱动处理
  • gpios属性：指定了 LED 连接的 GPIO 控制器（&gpx1）、引脚号（0）和有效电平（GPIO_ACTIVE_HIGH或 GPIO_ACTIVE_LOW）。
  • default-state = "off"定义设备的默认状态为关闭。
  • 设备树源文件（.dts）会被编译成二进制格式（.dtb），并由 Bootloader 在启动时加载到内存中传递给内核。


控制

LED 设备树节点的 label属性决定了其在 /sys/class/leds/下的目录名，以上配置可得：

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root@iTop4412_Ubuntu16:/home/easy$ ls /sys/class/leds
mmc0::  red:system  red:user

通过 /sys 节点控制

写入 1点亮，0熄灭。

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echo 1 > /sys/class/leds/red:user/brightness
echo 0 > /sys/class/leds/red:user/brightness

通过 C 程序控制

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#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
int main() {
    int fd = open("/sys/class/leds/red:user/brightness", O_WRONLY);
    write(fd, "1", 1);  // 点亮
    sleep(1);
    write(fd, "0", 1);   // 熄灭
    close(fd);
    return 0;
}

以上 2 种控制方式均需要 root 权限操作 sysfs 文件。


代码分析

整体流程

  1. dts 被编译成 dtb，dtb 烧录到存储卡后，在 uboot 中被加载到内存，并将首地址通过参数传给 kernel。
  2. 解析 dtb，dtb 被解析为 device_node 节点。
  3. 初始化 bus，注册 platform_bus 和 platform_bus_type。
  4. 初始化 driver。
  5. 匹配 device。
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// @ init/main.c
void __init start_kernel(void)
{
    // 1
    setup_arch(&command_line);	// @ arch/arm/kernel/setup.c
    	// -> unflatten_device_tree();	@ drivers/of/fdt.c
    
    // 2
    rest_init();
    	// -> pid = kernel_thread(kernel_init, NULL, CLONE_FS);
    		// -> kernel_init_freeable();
    			// -> do_basic_setup();
    				// -> driver_init();
    					// -> devices_init();	@ drivers/base/init.c
    					// -> buses_init();
    					// -> classes_init();
    					// -> of_core_init();
    					// -> platform_bus_init();
    						// -> device_register(&platform_bus);	@ drivers/base/platform.c
    						// -> bus_register(&platform_bus_type);
    // 3
    				// -> do_initcalls();
    					// #define arch_initcall(fn)		__define_initcall(fn, 3)
    					// arch_initcall_sync(of_platform_default_populate_init);	@ drivers/of/platform.c
    					// #define device_initcall(fn)		__define_initcall(fn, 6)
    					// module_platform_driver(gpio_led_driver);	@ drivers/leds/leds-gpio.c
}

dtb 解析

获取 machine_desc

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// @ arch/arm/kernel/setup.c
void __init setup_arch(char **cmdline_p)
{
	const struct machine_desc *mdesc;

	setup_processor();
	mdesc = setup_machine_fdt(__atags_pointer);
	if (!mdesc)
		mdesc = setup_machine_tags(__atags_pointer, __machine_arch_type);
	if (!mdesc) {
		early_print("\nError: invalid dtb and unrecognized/unsupported machine ID\n");
		early_print("  r1=0x%08x, r2=0x%08x\n", __machine_arch_type,
			    __atags_pointer);
		if (__atags_pointer)
			early_print("  r2[]=%*ph\n", 16,
				    phys_to_virt(__atags_pointer));
		dump_machine_table();
	}
    ...

  • setup_machine_fdt(__atags_pointer); 根据设备树根节点的 compatible 属性匹配 machine_desc 结构体，确定硬件平台（如开发板型号）。__atags_pointer是设备树物理地址，由Bootloader传入。

  • setup_machine_tags(__atags_pointer, __machine_arch_type);若设备树解析失败，通过传统 tag 列表（如ATAGS）匹配 machine_desc（旧式启动传参）。

  • 还是失败，则输出当前的 machine_arch_type、atags_pointer 地址，分别存在在 r1、r2 寄存器。

转为 device_node tree

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// @ of.h
/* Pointer for first entry in chain of all nodes. */
extern struct device_node *of_root;
extern struct device_node *of_chosen;
extern struct device_node *of_aliases;
extern struct device_node *of_stdout;

// base.c
LIST_HEAD(aliases_lookup);
struct device_node *of_root;
EXPORT_SYMBOL(of_root);
struct device_node *of_chosen;
struct device_node *of_aliases;
struct device_node *of_stdout;
static const char *of_stdout_options;
struct kset *of_kset;

// fdt.c
void *initial_boot_params;
static void * __init early_init_dt_alloc_memory_arch(u64 size, u64 align)
{
	return memblock_virt_alloc(size, align);
}

/**
 * @blob: The blob to expand
 * @dad: Parent device node
 * @mynodes: The device_node tree created by the call
 * @dt_alloc: An allocator that provides a virtual address to memory
 * for the resulting tree
 * @detached: if true set OF_DETACHED on @mynodes
 *
 * Returns NULL on failure or the memory chunk containing the unflattened
 * device tree on success.
 */
void *__unflatten_device_tree(const void *blob,
			      struct device_node *dad,
			      struct device_node **mynodes,
			      void *(*dt_alloc)(u64 size, u64 align),
			      bool detached){}

/**
 * unflatten_device_tree - create tree of device_nodes from flat blob
 *
 * unflattens the device-tree passed by the firmware, creating the
 * tree of struct device_node. It also fills the "name" and "type"
 * pointers of the nodes so the normal device-tree walking functions
 * can be used.
 */
void __init unflatten_device_tree(void)
{
	__unflatten_device_tree(initial_boot_params, NULL, &of_root,
				early_init_dt_alloc_memory_arch, false);
	...
}

初始化 bus

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// @ drivers/base/platform.c
struct device platform_bus = {
	.init_name	= "platform",
};
EXPORT_SYMBOL_GPL(platform_bus);

struct bus_type platform_bus_type = {
	.name		= "platform",
	.dev_groups	= platform_dev_groups,
	.match		= platform_match,
	.uevent		= platform_uevent,
	.dma_configure	= platform_dma_configure,
	.pm		= &platform_dev_pm_ops,
};
EXPORT_SYMBOL_GPL(platform_bus_type);

int __init platform_bus_init(void)
{
    device_register(&platform_bus);
    bus_register(&platform_bus_type);
}

driver 注册过程

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// drivers/leds/leds-gpio.c
static const struct of_device_id of_gpio_leds_match[] = {
	{ .compatible = "gpio-leds", },
	{},
};

static struct platform_driver gpio_led_driver = {
	.probe		= gpio_led_probe,
	.shutdown	= gpio_led_shutdown,
	.driver		= {
		.name	= "leds-gpio",
		.of_match_table = of_gpio_leds_match,
	},
};

module_platform_driver(gpio_led_driver);

module_platform_driver 展开

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// @ include/linux/platform_device.h
/* module_platform_driver() - Helper macro for drivers that don't do
 * anything special in module init/exit.  This eliminates a lot of
 * boilerplate.  Each module may only use this macro once, and
 * calling it replaces module_init() and module_exit()
 */
#define module_platform_driver(__platform_driver) \
	module_driver(__platform_driver, platform_driver_register, \
			platform_driver_unregister)

// @ include/linux/device.h
/**
 * module_driver() - Helper macro for drivers that don't do anything
 * special in module init/exit. This eliminates a lot of boilerplate.
 * Each module may only use this macro once, and calling it replaces
 * module_init() and module_exit().
 *
 * @__driver: driver name
 * @__register: register function for this driver type
 * @__unregister: unregister function for this driver type
 * @...: Additional arguments to be passed to __register and __unregister.
 *
 * Use this macro to construct bus specific macros for registering
 * drivers, and do not use it on its own.
 */
#define module_driver(__driver, __register, __unregister, ...) \
static int __init __driver##_init(void) \
{ \
	return __register(&(__driver) , ##__VA_ARGS__); \
} \
module_init(__driver##_init); \
static void __exit __driver##_exit(void) \
{ \
	__unregister(&(__driver) , ##__VA_ARGS__); \
} \
module_exit(__driver##_exit);

// @ include/linux/module.h
/**
 * module_init() - driver initialization entry point
 * @x: function to be run at kernel boot time or module insertion
 *
 * module_init() will either be called during do_initcalls() (if
 * builtin) or at module insertion time (if a module).  There can only
 * be one per module.
 */
#define module_init(x)	__initcall(x);
/**
 * module_exit() - driver exit entry point
 * @x: function to be run when driver is removed
 *
 * module_exit() will wrap the driver clean-up code
 * with cleanup_module() when used with rmmod when
 * the driver is a module.  If the driver is statically
 * compiled into the kernel, module_exit() has no effect.
 * There can only be one per module.
 */
#define module_exit(x)	__exitcall(x);

// @ include/linux/init.h
/*
 * initcalls are now grouped by functionality into separate
 * subsections. Ordering inside the subsections is determined
 * by link order. 
 * For backwards compatibility, initcall() puts the call in 
 * the device init subsection.
 *
 * The `id' arg to __define_initcall() is needed so that multiple initcalls
 * can point at the same handler without causing duplicate-symbol build errors.
 *
 * Initcalls are run by placing pointers in initcall sections that the
 * kernel iterates at runtime. The linker can do dead code / data elimination
 * and remove that completely, so the initcall sections have to be marked
 * as KEEP() in the linker script.
 */
#define ___define_initcall(fn, id, __sec) \
	static initcall_t __initcall_##fn##id __used \
		__attribute__((__section__(#__sec ".init"))) = fn;
#define __define_initcall(fn, id) ___define_initcall(fn, id, .initcall##id)
#define device_initcall(fn)		__define_initcall(fn, 6)
#define __initcall(fn) device_initcall(fn)
#define __exitcall(fn)						\
	static exitcall_t __exitcall_##fn __exit_call = fn

所以 module_platform_driver(gpio_led_driver); 会被展开成：

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// 1
module_driver(gpio_led_driver, platform_driver_register, platform_driver_unregister);

// 2
static int __init gpio_led_driver_init(void)
{
    return platform_driver_register(&gpio_led_driver);
}
module_init(gpio_led_driver_init);

static void __exit gpio_led_driver_exit(void)
{
    platform_driver_unregister(&gpio_led_driver);
}
module_exit(gpio_led_driver_exit);

// 3 gpio_led_driver_init/gpio_led_driver_exit 不再展开
__initcall(gpio_led_driver_init);
__exitcall(gpio_led_driver_exit);

// 4
__define_initcall(gpio_led_driver_init, 6);		// ___define_initcall(gpio_led_driver_init, 6, .initcall6)
static exitcall_t __exitcall_gpio_led_driver_exit __exit_call = gpio_led_driver_exit;

// 5
static initcall_t __initcall_gpio_led_driver_init6 __used \
    __attribute__((__section__(.initcall6 ".init"))) = gpio_led_driver_init;
static exitcall_t __exitcall_gpio_led_driver_exit __used __section(.exitcall.exit) = gpio_led_driver_exit;

platform_driver_register 到 platform_match

注册平台驱动时（platform_driver_register(&gpio_led_driver);），会触发 platform_match。

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// @ include/linux/platform_device.h
#define platform_driver_register(drv) \
	__platform_driver_register(drv, THIS_MODULE)

// @ drivers/base/platform.c
/**
 * __platform_driver_register - register a driver for platform-level devices
 * @drv: platform driver structure
 * @owner: owning module/driver
 */
int __platform_driver_register(struct platform_driver *drv,
				struct module *owner)
{
	drv->driver.owner = owner;
	drv->driver.bus = &platform_bus_type;
	drv->driver.probe = platform_drv_probe;
	drv->driver.remove = platform_drv_remove;
	drv->driver.shutdown = platform_drv_shutdown;

	return driver_register(&drv->driver);
}
EXPORT_SYMBOL_GPL(__platform_driver_register);

// @ drivers/base/driver.c
/**
 * driver_register - register driver with bus
 * @drv: driver to register
 *
 * We pass off most of the work to the bus_add_driver() call,
 * since most of the things we have to do deal with the bus
 * structures.
 */
int driver_register(struct device_driver *drv)
{
	int ret;
	struct device_driver *other;

	if (!drv->bus->p) {
		pr_err("Driver '%s' was unable to register with bus_type '%s' because the bus was not initialized.\n",
			   drv->name, drv->bus->name);
		return -EINVAL;
	}

	if ((drv->bus->probe && drv->probe) ||
	    (drv->bus->remove && drv->remove) ||
	    (drv->bus->shutdown && drv->shutdown))
		printk(KERN_WARNING "Driver '%s' needs updating - please use "
			"bus_type methods\n", drv->name);

	other = driver_find(drv->name, drv->bus);
	if (other) {
		printk(KERN_ERR "Error: Driver '%s' is already registered, "
			"aborting...\n", drv->name);
		return -EBUSY;
	}

	ret = bus_add_driver(drv);
	if (ret)
		return ret;
	ret = driver_add_groups(drv, drv->groups);
	if (ret) {
		bus_remove_driver(drv);
		return ret;
	}
	kobject_uevent(&drv->p->kobj, KOBJ_ADD);

	return ret;
}
EXPORT_SYMBOL_GPL(driver_register);

// @ drivers/base/driver.c
/**
 * driver_find - locate driver on a bus by its name.
 * @name: name of the driver.
 * @bus: bus to scan for the driver.
 *
 * Call kset_find_obj() to iterate over list of drivers on
 * a bus to find driver by name. Return driver if found.
 *
 * This routine provides no locking to prevent the driver it returns
 * from being unregistered or unloaded while the caller is using it.
 * The caller is responsible for preventing this.
 */
struct device_driver *driver_find(const char *name, struct bus_type *bus)
{
	struct kobject *k = kset_find_obj(bus->p->drivers_kset, name);
	struct driver_private *priv;

	if (k) {
		/* Drop reference added by kset_find_obj() */
		kobject_put(k);
		priv = to_driver(k);
		return priv->driver;
	}
	return NULL;
}
EXPORT_SYMBOL_GPL(driver_find);

// @ drivers/base/bus.c
/**
 * bus_add_driver - Add a driver to the bus.
 * @drv: driver.
 */
int bus_add_driver(struct device_driver *drv)
{
	struct bus_type *bus;
	struct driver_private *priv;
	int error = 0;

	bus = bus_get(drv->bus);
	if (!bus)
		return -EINVAL;

	pr_debug("bus: '%s': add driver %s\n", bus->name, drv->name);

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv) {
		error = -ENOMEM;
		goto out_put_bus;
	}
	klist_init(&priv->klist_devices, NULL, NULL);
	priv->driver = drv;
	drv->p = priv;
	priv->kobj.kset = bus->p->drivers_kset;
	error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,
				     "%s", drv->name);
	if (error)
		goto out_unregister;

	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
	if (drv->bus->p->drivers_autoprobe) {
		if (driver_allows_async_probing(drv)) {
			pr_debug("bus: '%s': probing driver %s asynchronously\n",
				drv->bus->name, drv->name);
			async_schedule(driver_attach_async, drv);
		} else {
			error = driver_attach(drv);
			if (error)
				goto out_unregister;
		}
	}
	module_add_driver(drv->owner, drv);

	error = driver_create_file(drv, &driver_attr_uevent);
	if (error) {
		printk(KERN_ERR "%s: uevent attr (%s) failed\n",
			__func__, drv->name);
	}
	error = driver_add_groups(drv, bus->drv_groups);
	if (error) {
		/* How the hell do we get out of this pickle? Give up */
		printk(KERN_ERR "%s: driver_create_groups(%s) failed\n",
			__func__, drv->name);
	}

	if (!drv->suppress_bind_attrs) {
		error = add_bind_files(drv);
		if (error) {
			/* Ditto */
			printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
				__func__, drv->name);
		}
	}

	return 0;

out_unregister:
	kobject_put(&priv->kobj);
	/* drv->p is freed in driver_release()  */
	drv->p = NULL;
out_put_bus:
	bus_put(bus);
	return error;
}

// @ drivers/base/dd.c
/**
 * driver_attach - try to bind driver to devices.
 * @drv: driver.
 *
 * Walk the list of devices that the bus has on it and try to
 * match the driver with each one.  If driver_probe_device()
 * returns 0 and the @dev->driver is set, we've found a
 * compatible pair.
 */
int driver_attach(struct device_driver *drv)
{
	return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
}
EXPORT_SYMBOL_GPL(driver_attach);

// @ drivers/base/bus.c
/**
 * bus_for_each_dev - device iterator.
 * @bus: bus type.
 * @start: device to start iterating from.
 * @data: data for the callback.
 * @fn: function to be called for each device.
 *
 * Iterate over @bus's list of devices, and call @fn for each,
 * passing it @data. If @start is not NULL, we use that device to
 * begin iterating from.
 *
 * We check the return of @fn each time. If it returns anything
 * other than 0, we break out and return that value.
 *
 * NOTE: The device that returns a non-zero value is not retained
 * in any way, nor is its refcount incremented. If the caller needs
 * to retain this data, it should do so, and increment the reference
 * count in the supplied callback.
 */
int bus_for_each_dev(struct bus_type *bus, struct device *start,
		     void *data, int (*fn)(struct device *, void *))
{
	struct klist_iter i;
	struct device *dev;
	int error = 0;

	if (!bus || !bus->p)
		return -EINVAL;

	klist_iter_init_node(&bus->p->klist_devices, &i,
			     (start ? &start->p->knode_bus : NULL));
	while (!error && (dev = next_device(&i)))
		error = fn(dev, data);
	klist_iter_exit(&i);
	return error;
}
EXPORT_SYMBOL_GPL(bus_for_each_dev);

// @ drivers/base/dd.c
static int __driver_attach(struct device *dev, void *data)
{
	struct device_driver *drv = data;
	int ret;

	/*
	 * Lock device and try to bind to it. We drop the error
	 * here and always return 0, because we need to keep trying
	 * to bind to devices and some drivers will return an error
	 * simply if it didn't support the device.
	 *
	 * driver_probe_device() will spit a warning if there
	 * is an error.
	 */

	ret = driver_match_device(drv, dev);
	if (ret == 0) {
		/* no match */
		return 0;
	} else if (ret == -EPROBE_DEFER) {
		dev_dbg(dev, "Device match requests probe deferral\n");
		driver_deferred_probe_add(dev);
		/*
		 * Driver could not match with device, but may match with
		 * another device on the bus.
		 */
		return 0;
	} else if (ret < 0) {
		dev_dbg(dev, "Bus failed to match device: %d\n", ret);
		/*
		 * Driver could not match with device, but may match with
		 * another device on the bus.
		 */
		return 0;
	} /* ret > 0 means positive match */

	if (dev->parent && dev->bus->need_parent_lock)
		device_lock(dev->parent);
	device_lock(dev);
	if (!dev->p->dead && !dev->driver)
		driver_probe_device(drv, dev);
	device_unlock(dev);
	if (dev->parent && dev->bus->need_parent_lock)
		device_unlock(dev->parent);

	return 0;
}

// drivers/base/base.h
static inline int driver_match_device(struct device_driver *drv,
				      struct device *dev)
{
	return drv->bus->match ? drv->bus->match(dev, drv) : 1;
}

// drv->bus->match == platform_match

以上代码的大致过程为：

  1. driver_find：查找 driver 是否已经存在于 bus，是则提示并结束注册流程。
  2. bus_add_driver：
    1. kobject_init_and_add：在Sysfs中创建对应的驱动对象 (kobject)，通常位于 /sys/bus/<bus_name>/drivers/下。
    2. klist_add_tail：将驱动添加到总线维护的驱动程序链表 (klist_drivers) 中。
    3. driver_attach：遍历总线上的所有设备，尝试将当前驱动与每个设备进行匹配。若匹配成功，则调用驱动的 probe函数。
    4. module_add_driver：增加该模块的引用计数，防止驱动在被设备使用时模块被意外卸载。
    5. driver_create_file：这会在 sysfs 对应的目录下（例如 /sys/bus/<bus_name>/drivers/<driver_name>/）创建一个名为 uevent的文件。
    6. driver_add_groups：将驱动程序本身定义的属性组（drv->groups）以及总线类型可能要求的默认属性组（bus->drv_groups）添加到 sysfs 中。
    7. add_bind_files：在sysfs 目录下创建 bind和 unbind文件。用户空间可以通过向这些文件写入设备号来动态地将设备绑定到该驱动或从该驱动解绑，为设备的热插拔和动态配置提供了灵活性。
  3. kobject_uevent：发送 KOBJ_ADD事件，通知用户空间有新驱动添加。

platform_match 匹配过程

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// @ drivers/base/platform.c
/**
 * 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);

	/* When driver_override is set, only bind to the matching driver */
	if (pdev->driver_override)
		return !strcmp(pdev->driver_override, drv->name);

	/* Attempt an OF style match first */
	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 */
	if (pdrv->id_table)
		return platform_match_id(pdrv->id_table, pdev) != NULL;

	/* fall-back to driver name match */
	return (strcmp(pdev->name, drv->name) == 0);
}

// @ include/linux/of_device.h
static inline int of_driver_match_device(struct device *dev,
					 const struct device_driver *drv)
{
	return of_match_device(drv->of_match_table, dev) != NULL;
}

// @ drivers/of/device.c
const struct of_device_id *of_match_device(const struct of_device_id *matches,
					   const struct device *dev)
{
	if ((!matches) || (!dev->of_node))
		return NULL;
	return of_match_node(matches, dev->of_node);
}
EXPORT_SYMBOL(of_match_device);

// @ drivers/of/base.c
/**
 * of_match_node - Tell if a device_node has a matching of_match structure
 *	@matches:	array of of device match structures to search in
 *	@node:		the of device structure to match against
 *
 *	Low level utility function used by device matching.
 */
const struct of_device_id *of_match_node(const struct of_device_id *matches,
					 const struct device_node *node)
{
	const struct of_device_id *match;
	unsigned long flags;

	raw_spin_lock_irqsave(&devtree_lock, flags);
	match = __of_match_node(matches, node);
	raw_spin_unlock_irqrestore(&devtree_lock, flags);
	return match;
}
EXPORT_SYMBOL(of_match_node);

// @ drivers/of/base.c
static
const struct of_device_id *__of_match_node(const struct of_device_id *matches,
					   const struct device_node *node)
{
	const struct of_device_id *best_match = NULL;
	int score, best_score = 0;

	if (!matches)
		return NULL;

	for (; matches->name[0] || matches->type[0] || matches->compatible[0]; matches++) {
		score = __of_device_is_compatible(node, matches->compatible,
						  matches->type, matches->name);
		if (score > best_score) {
			best_match = matches;
			best_score = score;
		}
	}

	return best_match;
}

// @ drivers/of/base.c
/**
 * __of_device_is_compatible() - Check if the node matches given constraints
 * @device: pointer to node
 * @compat: required compatible string, NULL or "" for any match
 * @type: required device_type value, NULL or "" for any match
 * @name: required node name, NULL or "" for any match
 *
 * 检查给定的@compat、@type和@name字符串是否与给定@device的属性匹配。
 * 通过传递NULL或空字符串作为约束，可以跳过约束。
 *
 * 不匹配时返回0，匹配时返回正整数。返回值是相对分数，较大的值表示更好的匹配。
 * 该分数针对给定的参数进行加权，以获得最高分数。匹配的实际优先级顺序如下：
 *
 * 1. specific compatible && type && name
 * 2. specific compatible && type
 * 3. specific compatible && name
 * 4. specific compatible
 * 5. general compatible && type && name
 * 6. general compatible && type
 * 7. general compatible && name
 * 8. general compatible
 * 9. type && name
 * 10. type
 * 11. name
 */
static int __of_device_is_compatible(const struct device_node *device,
				     const char *compat, const char *type, const char *name)
{
	struct property *prop;
	const char *cp;
	int index = 0, score = 0;

	/* Compatible match has highest priority */
	if (compat && compat[0]) {
		prop = __of_find_property(device, "compatible", NULL);
		for (cp = of_prop_next_string(prop, NULL); cp;
		     cp = of_prop_next_string(prop, cp), index++) {
			if (of_compat_cmp(cp, compat, strlen(compat)) == 0) {
				score = INT_MAX/2 - (index << 2);
				break;
			}
		}
		if (!score)
			return 0;
	}

	/* Matching type is better than matching name */
	if (type && type[0]) {
		if (!device->type || of_node_cmp(type, device->type))
			return 0;
		score += 2;
	}

	/* Matching name is a bit better than not */
	if (name && name[0]) {
		if (!device->name || of_node_cmp(name, device->name))
			return 0;
		score++;
	}

	return score;
}

driver_probe_device

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// @ drivers/base/dd.c
/**
 * driver_probe_device - attempt to bind device & driver together
 * @drv: driver to bind a device to
 * @dev: device to try to bind to the driver
 *
 * This function returns -ENODEV if the device is not registered,
 * 1 if the device is bound successfully and 0 otherwise.
 *
 * This function must be called with @dev lock held.  When called for a
 * USB interface, @dev->parent lock must be held as well.
 *
 * If the device has a parent, runtime-resume the parent before driver probing.
 */
int driver_probe_device(struct device_driver *drv, struct device *dev)
{
	int ret = 0;

	if (!device_is_registered(dev))
		return -ENODEV;

	pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
		 drv->bus->name, __func__, dev_name(dev), drv->name);

	pm_runtime_get_suppliers(dev);
	if (dev->parent)
		pm_runtime_get_sync(dev->parent);

	pm_runtime_barrier(dev);
	if (initcall_debug)
		ret = really_probe_debug(dev, drv);
	else
		ret = really_probe(dev, drv);
	pm_request_idle(dev);

	if (dev->parent)
		pm_runtime_put(dev->parent);

	pm_runtime_put_suppliers(dev);
	return ret;
}

// @ drivers/base/dd.c
static int really_probe(struct device *dev, struct device_driver *drv)
{
	int ret = -EPROBE_DEFER;
	int local_trigger_count = atomic_read(&deferred_trigger_count);
	bool test_remove = IS_ENABLED(CONFIG_DEBUG_TEST_DRIVER_REMOVE) &&
			   !drv->suppress_bind_attrs;

	if (defer_all_probes) {
		/*
		 * Value of defer_all_probes can be set only by
		 * device_defer_all_probes_enable() which, in turn, will call
		 * wait_for_device_probe() right after that to avoid any races.
		 */
		dev_dbg(dev, "Driver %s force probe deferral\n", drv->name);
		driver_deferred_probe_add(dev);
		return ret;
	}

	ret = device_links_check_suppliers(dev);
	if (ret == -EPROBE_DEFER)
		driver_deferred_probe_add_trigger(dev, local_trigger_count);
	if (ret)
		return ret;

	atomic_inc(&probe_count);
	pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
		 drv->bus->name, __func__, drv->name, dev_name(dev));
	if (!list_empty(&dev->devres_head)) {
		dev_crit(dev, "Resources present before probing\n");
		ret = -EBUSY;
		goto done;
	}

re_probe:
	dev->driver = drv;

	/* If using pinctrl, bind pins now before probing */
	ret = pinctrl_bind_pins(dev);
	if (ret)
		goto pinctrl_bind_failed;

	ret = dma_configure(dev);
	if (ret)
		goto probe_failed;

	if (driver_sysfs_add(dev)) {
		printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
			__func__, dev_name(dev));
		goto probe_failed;
	}

	if (dev->pm_domain && dev->pm_domain->activate) {
		ret = dev->pm_domain->activate(dev);
		if (ret)
			goto probe_failed;
	}

	if (dev->bus->probe) {
		ret = dev->bus->probe(dev);
		if (ret)
			goto probe_failed;
	} else if (drv->probe) {
		ret = drv->probe(dev);
		if (ret)
			goto probe_failed;
	}

	if (test_remove) {
		test_remove = false;

		if (dev->bus->remove)
			dev->bus->remove(dev);
		else if (drv->remove)
			drv->remove(dev);

		devres_release_all(dev);
		driver_sysfs_remove(dev);
		dev->driver = NULL;
		dev_set_drvdata(dev, NULL);
		if (dev->pm_domain && dev->pm_domain->dismiss)
			dev->pm_domain->dismiss(dev);
		pm_runtime_reinit(dev);

		goto re_probe;
	}

	pinctrl_init_done(dev);

	if (dev->pm_domain && dev->pm_domain->sync)
		dev->pm_domain->sync(dev);

	driver_bound(dev);
	ret = 1;
	pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
		 drv->bus->name, __func__, dev_name(dev), drv->name);
	goto done;

probe_failed:
	if (dev->bus)
		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
					     BUS_NOTIFY_DRIVER_NOT_BOUND, dev);
pinctrl_bind_failed:
	device_links_no_driver(dev);
	devres_release_all(dev);
	dma_deconfigure(dev);
	driver_sysfs_remove(dev);
	dev->driver = NULL;
	dev_set_drvdata(dev, NULL);
	if (dev->pm_domain && dev->pm_domain->dismiss)
		dev->pm_domain->dismiss(dev);
	pm_runtime_reinit(dev);
	dev_pm_set_driver_flags(dev, 0);

	switch (ret) {
	case -EPROBE_DEFER:
		/* Driver requested deferred probing */
		dev_dbg(dev, "Driver %s requests probe deferral\n", drv->name);
		driver_deferred_probe_add_trigger(dev, local_trigger_count);
		break;
	case -ENODEV:
	case -ENXIO:
		pr_debug("%s: probe of %s rejects match %d\n",
			 drv->name, dev_name(dev), ret);
		break;
	default:
		/* driver matched but the probe failed */
		printk(KERN_WARNING
		       "%s: probe of %s failed with error %d\n",
		       drv->name, dev_name(dev), ret);
	}
	/*
	 * Ignore errors returned by ->probe so that the next driver can try
	 * its luck.
	 */
	ret = 0;
done:
	atomic_dec(&probe_count);
	wake_up_all(&probe_waitqueue);
	return ret;
}

  • 首先初始化 pin： pinctrl_bind_pins(dev);

  • 再初始化 dma：dma_configure(dev);

  • 初始化 sysfs：driver_sysfs_add(dev)

  • 执行：drv->probe(dev);，即为 gpio_led_probe。

gpio_led_probe

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// @ drivers/leds/leds-gpio.c
static int gpio_led_probe(struct platform_device *pdev)
{
	struct gpio_led_platform_data *pdata = dev_get_platdata(&pdev->dev);
	struct gpio_leds_priv *priv;
	int i, ret = 0;

	if (pdata && pdata->num_leds) {
		priv = devm_kzalloc(&pdev->dev,
				sizeof_gpio_leds_priv(pdata->num_leds),
					GFP_KERNEL);
		if (!priv)
			return -ENOMEM;

		priv->num_leds = pdata->num_leds;
		for (i = 0; i < priv->num_leds; i++) {
			ret = create_gpio_led(&pdata->leds[i], &priv->leds[i],
					      &pdev->dev, NULL,
					      pdata->gpio_blink_set);
			if (ret < 0)
				return ret;
		}
	} else {
		priv = gpio_leds_create(pdev);
		if (IS_ERR(priv))
			return PTR_ERR(priv);
	}

	platform_set_drvdata(pdev, priv);

	return 0;
}

// @ drivers/leds/leds-gpio.c
static int create_gpio_led(const struct gpio_led *template,
	struct gpio_led_data *led_dat, struct device *parent,
	struct device_node *np, gpio_blink_set_t blink_set)
{
	int ret, state;

	led_dat->gpiod = template->gpiod;
	if (!led_dat->gpiod) {
		/*
		 * This is the legacy code path for platform code that
		 * still uses GPIO numbers. Ultimately we would like to get
		 * rid of this block completely.
		 */
		unsigned long flags = GPIOF_OUT_INIT_LOW;

		/* skip leds that aren't available */
		if (!gpio_is_valid(template->gpio)) {
			dev_info(parent, "Skipping unavailable LED gpio %d (%s)\n",
					template->gpio, template->name);
			return 0;
		}

		if (template->active_low)
			flags |= GPIOF_ACTIVE_LOW;

		ret = devm_gpio_request_one(parent, template->gpio, flags,
					    template->name);
		if (ret < 0)
			return ret;

		led_dat->gpiod = gpio_to_desc(template->gpio);
		if (!led_dat->gpiod)
			return -EINVAL;
	}

	led_dat->cdev.name = template->name;
	led_dat->cdev.default_trigger = template->default_trigger;
	led_dat->can_sleep = gpiod_cansleep(led_dat->gpiod);
	if (!led_dat->can_sleep)
		led_dat->cdev.brightness_set = gpio_led_set;
	else
		led_dat->cdev.brightness_set_blocking = gpio_led_set_blocking;
	led_dat->blinking = 0;
	if (blink_set) {
		led_dat->platform_gpio_blink_set = blink_set;
		led_dat->cdev.blink_set = gpio_blink_set;
	}
	if (template->default_state == LEDS_GPIO_DEFSTATE_KEEP) {
		state = gpiod_get_value_cansleep(led_dat->gpiod);
		if (state < 0)
			return state;
	} else {
		state = (template->default_state == LEDS_GPIO_DEFSTATE_ON);
	}
	led_dat->cdev.brightness = state ? LED_FULL : LED_OFF;
	if (!template->retain_state_suspended)
		led_dat->cdev.flags |= LED_CORE_SUSPENDRESUME;
	if (template->panic_indicator)
		led_dat->cdev.flags |= LED_PANIC_INDICATOR;
	if (template->retain_state_shutdown)
		led_dat->cdev.flags |= LED_RETAIN_AT_SHUTDOWN;

	ret = gpiod_direction_output(led_dat->gpiod, state);
	if (ret < 0)
		return ret;

	return devm_of_led_classdev_register(parent, np, &led_dat->cdev);
}

// @ drivers/leds/led-class.c
/**
 * devm_of_led_classdev_register - resource managed led_classdev_register()
 *
 * @parent: parent of LED device
 * @led_cdev: the led_classdev structure for this device.
 */
int devm_of_led_classdev_register(struct device *parent,
				  struct device_node *np,
				  struct led_classdev *led_cdev)
{
	struct led_classdev **dr;
	int rc;

	dr = devres_alloc(devm_led_classdev_release, sizeof(*dr), GFP_KERNEL);
	if (!dr)
		return -ENOMEM;

	rc = of_led_classdev_register(parent, np, led_cdev);
	if (rc) {
		devres_free(dr);
		return rc;
	}

	*dr = led_cdev;
	devres_add(parent, dr);

	return 0;
}
EXPORT_SYMBOL_GPL(devm_of_led_classdev_register);

// @ drivers/leds/led-class.c
/**
 * of_led_classdev_register - register a new object of led_classdev class.
 *
 * @parent: parent of LED device
 * @led_cdev: the led_classdev structure for this device.
 * @np: DT node describing this LED
 */
int of_led_classdev_register(struct device *parent, struct device_node *np,
			    struct led_classdev *led_cdev)
{
	char name[LED_MAX_NAME_SIZE];
	int ret;

	ret = led_classdev_next_name(led_cdev->name, name, sizeof(name));
	if (ret < 0)
		return ret;

	mutex_init(&led_cdev->led_access);
	mutex_lock(&led_cdev->led_access);
	led_cdev->dev = device_create_with_groups(leds_class, parent, 0,
				led_cdev, led_cdev->groups, "%s", name);
	if (IS_ERR(led_cdev->dev)) {
		mutex_unlock(&led_cdev->led_access);
		return PTR_ERR(led_cdev->dev);
	}
	led_cdev->dev->of_node = np;

	if (ret)
		dev_warn(parent, "Led %s renamed to %s due to name collision",
				led_cdev->name, dev_name(led_cdev->dev));

	if (led_cdev->flags & LED_BRIGHT_HW_CHANGED) {
		ret = led_add_brightness_hw_changed(led_cdev);
		if (ret) {
			device_unregister(led_cdev->dev);
			mutex_unlock(&led_cdev->led_access);
			return ret;
		}
	}

	led_cdev->work_flags = 0;
#ifdef CONFIG_LEDS_TRIGGERS
	init_rwsem(&led_cdev->trigger_lock);
#endif
#ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED
	led_cdev->brightness_hw_changed = -1;
#endif
	/* add to the list of leds */
	down_write(&leds_list_lock);
	list_add_tail(&led_cdev->node, &leds_list);
	up_write(&leds_list_lock);

	if (!led_cdev->max_brightness)
		led_cdev->max_brightness = LED_FULL;

	led_update_brightness(led_cdev);

	led_init_core(led_cdev);

#ifdef CONFIG_LEDS_TRIGGERS
	led_trigger_set_default(led_cdev);
#endif

	mutex_unlock(&led_cdev->led_access);

	dev_dbg(parent, "Registered led device: %s\n",
			led_cdev->name);

	return 0;
}
EXPORT_SYMBOL_GPL(of_led_classdev_register);

// @ drivers/base/core.c
/**
 * device_create_with_groups - creates a device and registers it with sysfs
 * @class: pointer to the struct class that this device should be registered to
 * @parent: pointer to the parent struct device of this new device, if any
 * @devt: the dev_t for the char device to be added
 * @drvdata: the data to be added to the device for callbacks
 * @groups: NULL-terminated list of attribute groups to be created
 * @fmt: string for the device's name
 *
 * This function can be used by char device classes.  A struct device
 * will be created in sysfs, registered to the specified class.
 * Additional attributes specified in the groups parameter will also
 * be created automatically.
 *
 * A "dev" file will be created, showing the dev_t for the device, if
 * the dev_t is not 0,0.
 * If a pointer to a parent struct device is passed in, the newly created
 * struct device will be a child of that device in sysfs.
 * The pointer to the struct device will be returned from the call.
 * Any further sysfs files that might be required can be created using this
 * pointer.
 *
 * Returns &struct device pointer on success, or ERR_PTR() on error.
 *
 * Note: the struct class passed to this function must have previously
 * been created with a call to class_create().
 */
struct device *device_create_with_groups(struct class *class,
					 struct device *parent, dev_t devt,
					 void *drvdata,
					 const struct attribute_group **groups,
					 const char *fmt, ...)
{
	va_list vargs;
	struct device *dev;

	va_start(vargs, fmt);
	dev = device_create_groups_vargs(class, parent, devt, drvdata, groups,
					 fmt, vargs);
	va_end(vargs);
	return dev;
}
EXPORT_SYMBOL_GPL(device_create_with_groups);

注册成功后，内核会在 /sys/class/leds/目录下为每个 LED 创建一个子目录。

参考

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      tags: true