Camera | 10.linux驱动 led架构-基于rk3568

前面文章我们简单给大家介绍了如何移植闪光灯芯片sgm3141，该驱动依赖了led子系统和v4l2子系统。

V4L2可以参考前面camera系列文章，本文主要讲述led子系统。

一、LED子系统框架

Linux内核的 led 子系统主要功能：

• 为每个设备在/sys/class/leds下创建不同的文件节点，用于操作led
• 抽象出所有的灯基本操作，设置亮、灭，光强、闪烁等

框架所处的位置，正如上图所示，由下往上看：

• Hardware：
  
  硬件设备，指的是LED，可以是各种设备上的led灯

• 硬件驱动层：
  
  是直接操作硬件的实现，用于驱动硬件，实现相应的功能，并且将硬件设备注册进框架之中。

• 核心层：
  
  将LED进行统一管理，向下提供注册接口，向上提供统一访问接口，方便用户访问

• 用户层：
  
  用户通过指定的文件节点，能够直接控制LED的亮灭。

不同的led位于不同的外设上，有的可能通过gpio控制，也可能由其他的芯片控制，

有的led只需要控制亮灭，有的需要设置为闪烁，只需要基于架构设置对应的回调函数即可。

二、LED子系统驱动文件

了解完LED子系统框架之后，我们来分析一下其相关的目录结构！

kernel
│   └── driver
│   │   └── leds
│   │   │   ├──Makefile
│   │   │   ├──led-core.c            *
│   │   │   ├──led-gpio.c
│   │   │   ├──led-class.c           *
│   │   │   ├──led-class-flash.c  *
│   │   │   ├──led-triggers.c       *
│   │   │   ├──......
│   │   │   └── trigger
│   │   │   │   ├── ledtrig-cpu.c
│   │   │   │   ├── ledtrig-heartbeat.c
│   │   │   │   ├── .......
include
│   └── linux
│   │  ├──leds.h    *
【*表示核心文件】

上面即为LED子系统的目录结构，其主要核心文件有：

• led-core.c：核心层实现，抽象软件实现的相关功能，如闪烁，亮度设置等等，并管理LED设备
• led-gpio.c：直接控制硬件设备，并且将其硬件设备注册进入LED驱动框架
• led-class.c：定义用户访问的相关接口
• led-class-flash.c：灯闪烁相关功能函数实现
• led-triggers.c：LED出发功能的抽象
• ledtrig-cpu.c：将LED作为CPU灯
• ledtrig-heartbeat.c：将LED作为心跳灯

打开了LED子系统目录下的kernel/drivers/leds/Makefile，我们看到

# SPDX-License-Identifier: GPL-2.0

# LED Core
obj-$(CONFIG_NEW_LEDS)+= led-core.o
obj-$(CONFIG_LEDS_CLASS)+= led-class.o
obj-$(CONFIG_LEDS_CLASS_FLASH)+= led-class-flash.o
obj-$(CONFIG_LEDS_TRIGGERS)+= led-triggers.o

我们必须在内核的配置中，通过 make menuconfig打开LED的相关配置，才支持LED相关功能。

三、查看sysfs文件结构

1. sys/class/leds/

我们在开发板中输入ls /sys/class/leds/，可以查看LED子系统生成的文件信息。

rk3568_r:/ # ls /sys/class/leds
blue  gpio-flash  green  mmc0::  red

• blue：板子的RGB灯的蓝色
• green：板子的RGB灯的绿色
• red: 板子的RGB灯的红色
• gpio-flash：camera gpio闪光灯
• mmc0:: ：SD卡指示灯

2. red等子目录

根据打开配置的不同，生成不同的文件节点,比如red目录下信息：

rk3568_r:/sys/class/leds # ls red
brightness  max_brightness  red_bri_reg  subsystem  uevent
device      power           red_delay    trigger

相关属性文件有：brightness、max_brightness、trigger等

1. max_brightness：表示LED灯的最大亮度值。
2. brightness：表示当前LED灯的亮度值，它的可取 值范围为[0~max_brightness]，一些LED设备不支持多级亮度，直接以非0值来 表示LED为点亮状态，0值表示灭状态。

@kernel/include/linux/leds.h
enum led_brightness {
 LED_OFF  = 0,    //全暗
 LED_HALF = 127,  //一半亮度
 LED_FULL = 255,  //最大亮度
};

1. delay_off、delay_on：trigger为timer时，LED亮灭的时间，单位ms
2. trigger：则指示了LED灯的触发方式，查看该文件的内容时，该文件会 列出它的所有可用触方式，而当前使用的触发方式会以“[]”符号括起。

常见的触 发方式如下表所示：

触发方式	说明
none	无触发方式
disk-activity	硬盘活动
nand-disk	nand flash活动
mtd	mtd设备活动
timer	定时器
heartbeat	系统心跳

1）点亮 LED

echo 255 > /sys/class/leds/red/brightness
cat /sys/class/leds/red/brightness
cat /sys/class/leds/red/max_brightness

2）关闭led

echo 0 > /sys/class/leds/red/delay_on
或
echo 0 > /sys/class/leds/red/brightness

3）这几个文件节点由下面宏表示，

@drivers/leds/led-class.c
static DEVICE_ATTR_RO(max_brightness);

#ifdef CONFIG_LEDS_TRIGGERS
static DEVICE_ATTR(trigger, 0644, led_trigger_show, led_trigger_store);
static struct attribute *led_trigger_attrs[] = {
	&dev_attr_trigger.attr,
	NULL,
};
static const struct attribute_group led_trigger_group = {
	.attrs = led_trigger_attrs,
};
#endif

static struct attribute *led_class_attrs[] = {
	&dev_attr_brightness.attr,
	&dev_attr_max_brightness.attr,
	NULL,
};

static const struct attribute_group led_group = {
	.attrs = led_class_attrs,
};

static const struct attribute_group *led_groups[] = {
	&led_group,
#ifdef CONFIG_LEDS_TRIGGERS
	&led_trigger_group,
#endif
	NULL,
};

创建位置：

int of_led_classdev_register(struct device *parent, struct device_node *np,
			    struct led_classdev *led_cdev)
{
	……
	led_cdev->dev = device_create_with_groups(leds_class, parent, 0,
				led_cdev, led_cdev->groups, "%s", name);
    ……
}

3. gpio-flash闪光灯目录

rk3568_r:/sys/class/leds/gpio-flash # ls
brightness  flash_strobe   max_brightness     power      trigger
device      flash_timeout  max_flash_timeout  subsystem  uevent

创建代码：

@drivers/leds/led-class-flash.c
static struct attribute *led_flash_strobe_attrs[] = {
	&dev_attr_flash_strobe.attr,
	NULL,
};

static struct attribute *led_flash_timeout_attrs[] = {
	&dev_attr_flash_timeout.attr,
	&dev_attr_max_flash_timeout.attr,
	NULL,
};

static struct attribute *led_flash_brightness_attrs[] = {
	&dev_attr_flash_brightness.attr,
	&dev_attr_max_flash_brightness.attr,
	NULL,
};

static struct attribute *led_flash_fault_attrs[] = {
	&dev_attr_flash_fault.attr,
	NULL,
};

static const struct attribute_group led_flash_strobe_group = {
	.attrs = led_flash_strobe_attrs,
};

static const struct attribute_group led_flash_timeout_group = {
	.attrs = led_flash_timeout_attrs,
};

static const struct attribute_group led_flash_brightness_group = {
	.attrs = led_flash_brightness_attrs,
};

static const struct attribute_group led_flash_fault_group = {
	.attrs = led_flash_fault_attrs,
};

注册代码

int led_classdev_flash_register(struct device *parent,
				struct led_classdev_flash *fled_cdev)
{
	……
	if (led_cdev->flags & LED_DEV_CAP_FLASH) {
		……
		/* Select the sysfs attributes to be created for the device */
		led_flash_init_sysfs_groups(fled_cdev);
	}

	/* Register led class device */
	ret = led_classdev_register(parent, led_cdev);
	……
}

测试gpio闪光灯

echo 1 > /sys/class/leds/gpio-flash/flash_strobe

注意，实际操作摄像头闪光灯，并不是通过sysfs下的文件节点操作，而是通过v4l2架构下发ioctl的命令来实现的

四、驱动解析

1. 结构体和注册函数

下面介绍led相关的重要的结构体

struct led_classdev {
	const char		*name;
	enum led_brightness	 brightness;       //光强
	enum led_brightness	 max_brightness;   //最大光强
	int			 flags;
	…………

	/* set_brightness_work / blink_timer flags, atomic, private. */
	unsigned long		work_flags;
     …………
	/* Set LED brightness level
	 * Must not sleep. Use brightness_set_blocking for drivers
	 * that can sleep while setting brightness.
	 */
	void		(*brightness_set)(struct led_classdev *led_cdev,
					  enum led_brightness brightness);  //设置光强
	/*
	 * Set LED brightness level immediately - it can block the caller for
	 * the time required for accessing a LED device register.
	 */
	int (*brightness_set_blocking)(struct led_classdev *led_cdev,
				       enum led_brightness brightness);
	/* Get LED brightness level */
	enum led_brightness (*brightness_get)(struct led_classdev *led_cdev); //获取光强

	/*
	 * Activate hardware accelerated blink, delays are in milliseconds
	 * and if both are zero then a sensible default should be chosen.
	 * The call should adjust the timings in that case and if it can't
	 * match the values specified exactly.
	 * Deactivate blinking again when the brightness is set to LED_OFF
	 * via the brightness_set() callback.
	 */
	int		(*blink_set)(struct led_classdev *led_cdev,
				     unsigned long *delay_on,
				     unsigned long *delay_off);

	struct device		*dev;
	const struct attribute_group	**groups;

	struct list_head	 node;			/* LED Device list */
	const char		*default_trigger;	/* Trigger to use */

	unsigned long		 blink_delay_on, blink_delay_off;
	struct timer_list	 blink_timer;
	int			 blink_brightness;
	int			 new_blink_brightness;
	void			(*flash_resume)(struct led_classdev *led_cdev);

	struct work_struct	set_brightness_work;
	int			delayed_set_value;

#ifdef CONFIG_LEDS_TRIGGERS
	/* Protects the trigger data below */
	struct rw_semaphore	 trigger_lock;

	struct led_trigger	*trigger;
	struct list_head	 trig_list;
	void			*trigger_data;
	/* true if activated - deactivate routine uses it to do cleanup */
	bool			activated;
#endif

#ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED
	int			 brightness_hw_changed;
	struct kernfs_node	*brightness_hw_changed_kn;
#endif

	/* Ensures consistent access to the LED Flash Class device */
	struct mutex		led_access;
};

该结构体包括led操作的所有信息，和回调函数

注册struct led_classdev结构图变量：

#define led_classdev_register(parent, led_cdev)				\
	of_led_classdev_register(parent, NULL, led_cdev)

对于gpio闪光灯，则需要填充一下结构体：

struct led_classdev_flash {
	/* led class device */
	struct led_classdev led_cdev;

	/* flash led specific ops */
	const struct led_flash_ops *ops;

	/* flash brightness value in microamperes along with its constraints */
	struct led_flash_setting brightness;

	/* flash timeout value in microseconds along with its constraints */
	struct led_flash_setting timeout;

	/* LED Flash class sysfs groups */
	const struct attribute_group *sysfs_groups[LED_FLASH_SYSFS_GROUPS_SIZE];
};

gpio闪光灯注册函数：

int led_classdev_flash_register(struct device *parent,
				struct led_classdev_flash *fled_cdev)

2. gpio闪光灯sgm3141驱动详解

看上图：

1. sgm3141驱动通过函数led_classdev_flash_register()->led_classdev_register()向led子系统注册该设备
2. sgm3141驱动通过函数v4l2_async_register_subdev()向v4l2子系统注册该设备
3. 如果用户直接通过/sys/class/leds/gpio-flash/flash_strobe文件操作led灯，则会直接调用struct led_flash_ops flash_ops的 .strobe_set方法，即sgm3141_led_flash_strobe_set()

操作log：

[  492.026391] sgm3141_led_flash_strobe_set+0x24/0x78
[  492.026453] flash_strobe_store+0x88/0xd8
[  492.026517] dev_attr_store+0x18/0x28
[  492.026571] sysfs_kf_write+0x48/0x58
[  492.026620] kernfs_fop_write+0xf4/0x220
[  492.026683] __vfs_write+0x34/0x158
[  492.026733] vfs_write+0xb0/0x1d0
[  492.026784] ksys_write+0x64/0xe0
[  492.026833] __arm64_sys_write+0x14/0x20
[  492.026867] el0_svc_common.constprop.0+0x64/0x178
[  492.026912] el0_svc_handler+0x28/0x78
[  492.026966] el0_svc+0x8/0xc

1. 如果用户的app拍照时操作闪光灯，则是通过v4l2子系统调用下发ioctl命令
   
   命令序列：

V4L2_CID_FLASH_LED_MODE ：设置led mod为 V4L2_FLASH_LED_MODE_TORCH(2),并点灯
V4L2_CID_FLASH_LED_MODE：到达指定超时时间（2.7秒），设置led mod为 V4L2_FLASH_LED_MODE_NONE 0
V4L2_CID_FLASH_LED_MODE：在此设置led mod为V4L2_FLASH_LED_MODE_FLASH(1)
V4L2_CID_FLASH_STROBE_STOP:停止闪光

操作log：

[   90.246203] sgm3141 V4L2_CID_FLASH_LED_MODE 2
[   90.246251] sgm3141_set_ctrl(),376
[   90.246262] sgm3141_set_output(),78 0
[   90.246277] sgm3141_set_output(),78 1

[   92.902746] sgm3141 V4L2_CID_FLASH_LED_MODE 0
[   92.902775] sgm3141_set_ctrl(),376
[   92.902781] sgm3141_set_output(),78 0

[   93.034903] sgm3141 V4L2_CID_FLASH_LED_MODE 1
[   93.034929] sgm3141_set_ctrl(),376
[   93.034934] sgm3141_set_output(),78 0
[   93.034943] sgm3141_led_flash_strobe_set(),166 state=1
[   93.034959] sgm3141_set_output(),78 1

[   93.034977] sgm3141 V4L2_CID_FLASH_STROBE_STOP 1
[   93.034988] sgm3141_set_ctrl(),406
[   93.034993] sgm3141_led_flash_strobe_set(),166 state=0
[   93.035002] sgm3141_set_output(),78 0
[   93.035058] sgm3141_timeout_work(),117

1. sgm驱动注册流程分析
   
   驱动架构基于platform总线，platform_driver 结构体如下：

static const struct of_device_id sgm3141_led_dt_match[] = {
	{ .compatible = "sgmicro,sgm3141" },
	{},
};
MODULE_DEVICE_TABLE(of, sgm3141_led_dt_match);

static struct platform_driver sgm3141_led_driver = {
	.probe		= sgm3141_led_probe,
	.remove		= sgm3141_led_remove,
	.driver		= {
		.name	= "sgm3141-flash",
		.of_match_table = sgm3141_led_dt_match,
	},
};