Camera | 10.linux驱动 led架构-基于rk3568-电源网星球号

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 Coreobj-$(CONFIG_NEW_LEDS)+= led-core.oobj-$(CONFIG_LEDS_CLASS)+= led-class.oobj-$(CONFIG_LEDS_CLASS_FLASH)+= led-class-flash.oobj-$(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/ledsblue  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 redbrightness  max_brightness  red_bri_reg  subsystem  ueventdevice      power           red_delay    trigger

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

max_brightness：表示LED灯的最大亮度值。
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.henum led_brightness { LED_OFF  = 0,    //全暗 LED_HALF = 127,  //一半亮度 LED_FULL = 255,  //最大亮度};

delay_off、delay_on：trigger为timer时，LED亮灭的时间，单位ms
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/brightnesscat /sys/class/leds/red/brightnesscat /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.cstatic DEVICE_ATTR_RO(max_brightness);#ifdef CONFIG_LEDS_TRIGGERSstatic 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,};#endifstatic 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 # lsbrightness  flash_strobe   max_brightness     power      triggerdevice      flash_timeout  max_flash_timeout  subsystem  uevent

创建代码：

@drivers/leds/led-class-flash.cstatic 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：

sgm3141驱动通过函数led_classdev_flash_register()->led_classdev_register()向led子系统注册该设备
sgm3141驱动通过函数v4l2_async_register_subdev()向v4l2子系统注册该设备
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

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 0V4L2_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

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, },};