前面文章我們簡單給大家介紹了如何移植閃光燈芯片sgm3141，該驅(qū)動依賴了led子系統(tǒng)和v4l2子系統(tǒng)。 V4L2可以參考前面camera系列文章，本文主要講述led子系統(tǒng)。

一、LED子系統(tǒng)框架

Linux內(nèi)核的 led 子系統(tǒng)主要功能：

• 為每個設(shè)備在/sys/class/leds下創(chuàng)建不同的文件節(jié)點，用于操作led
• 抽象出所有的燈基本操作，設(shè)置亮、滅，光強、閃爍等

框架所處的位置，正如上圖所示，由下往上看：

• Hardware： 硬件設(shè)備，指的是LED，可以是各種設(shè)備上的led燈

• 硬件驅(qū)動層： 是直接操作硬件的實現(xiàn)，用于驅(qū)動硬件，實現(xiàn)相應(yīng)的功能，并且將硬件設(shè)備注冊進框架之中。

• 核心層： 將LED進行統(tǒng)一管理，向下提供注冊接口，向上提供統(tǒng)一訪問接口，方便用戶訪問

• 用戶層： 用戶通過指定的文件節(jié)點，能夠直接控制LED的亮滅。

不同的led位于不同的外設(shè)上，有的可能通過gpio控制，也可能由其他的芯片控制， 有的led只需要控制亮滅，有的需要設(shè)置為閃爍，只需要基于架構(gòu)設(shè)置對應(yīng)的回調(diào)函數(shù)即可。

二、LED子系統(tǒng)驅(qū)動文件

了解完LED子系統(tǒng)框架之后，我們來分析一下其相關(guān)的目錄結(jié)構(gòu)！

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】

上面即為LED子系統(tǒng)的目錄結(jié)構(gòu)，其主要核心文件有：

• led-core.c：核心層實現(xiàn)，抽象軟件實現(xiàn)的相關(guān)功能，如閃爍，亮度設(shè)置等等，并管理LED設(shè)備
• led-gpio.c：直接控制硬件設(shè)備，并且將其硬件設(shè)備注冊進入LED驅(qū)動框架
• led-class.c：定義用戶訪問的相關(guān)接口
• led-class-flash.c：燈閃爍相關(guān)功能函數(shù)實現(xiàn)
• led-triggers.c：LED出發(fā)功能的抽象
• ledtrig-cpu.c：將LED作為CPU燈
• ledtrig-heartbeat.c：將LED作為心跳燈

打開了LED子系統(tǒng)目錄下的kernel/drivers/leds/Makefile，我們看到

# 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

我們必須在內(nèi)核的配置中，通過 make menuconfig打開LED的相關(guān)配置，才支持LED相關(guān)功能。

三、查看sysfs文件結(jié)構(gòu)

1. sys/class/leds/

我們在開發(fā)板中輸入ls /sys/class/leds/，可以查看LED子系統(tǒng)生成的文件信息。

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

• blue：板子的RGB燈的藍色
• green：板子的RGB燈的綠色
• red: 板子的RGB燈的紅色
• gpio-flash：camera gpio閃光燈
• mmc0:: ：SD卡指示燈

2. red等子目錄

根據(jù)打開配置的不同，生成不同的文件節(jié)點,比如red目錄下信息：

rk3568_r:/sys/class/leds # ls redbrightness  max_brightness  red_bri_reg  subsystem  ueventdevice      power           red_delay    trigger

相關(guān)屬性文件有：brightness、max_brightness、trigger等

1. max_brightness：表示LED燈的最大亮度值。
2. brightness：表示當(dāng)前LED燈的亮度值，它的可取 值范圍為[0~max_brightness]，一些LED設(shè)備不支持多級亮度，直接以非0值來 表示LED為點亮狀態(tài)，0值表示滅狀態(tài)。

@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};

1. delay_off、delay_on：trigger為timer時，LED亮滅的時間，單位ms
2. trigger：則指示了LED燈的觸發(fā)方式，查看該文件的內(nèi)容時，該文件會 列出它的所有可用觸方式，而當(dāng)前使用的觸發(fā)方式會以“[]”符號括起。

常見的觸 發(fā)方式如下表所示：

觸發(fā)方式 說明 none 無觸發(fā)方式 disk-activity 硬盤活動 nand-disk nand flash活動 mtd mtd設(shè)備活動 timer 定時器 heartbeat 系統(tǒng)心跳 1）點亮 LED

echo 255 > /sys/class/leds/red/brightnesscat /sys/class/leds/red/brightnesscat /sys/class/leds/red/max_brightness

2）關(guān)閉led

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

3）這幾個文件節(jié)點由下面宏表示，

@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,};

創(chuàng)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閃光燈目錄

rk3568_r:/sys/class/leds/gpio-flash # lsbrightness  flash_strobe   max_brightness     power      triggerdevice      flash_timeout  max_flash_timeout  subsystem  uevent

創(chuàng)建代碼：

@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,};

注冊代碼

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); ……}

測試gpio閃光燈

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

“

注意，實際操作攝像頭閃光燈，并不是通過sysfs下的文件節(jié)點操作，而是通過v4l2架構(gòu)下發(fā)ioctl的命令來實現(xiàn)的

”

四、驅(qū)動解析

1. 結(jié)構(gòu)體和注冊函數(shù)

下面介紹led相關(guān)的重要的結(jié)構(gòu)體

struct led_classdev { const char  *name; enum led_brightness  brightness;       //光強 enum led_brightness  max_brightness;   //最大光強 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);  //設(shè)置光強 /*  * 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); //獲取光強 /*  * 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;};

該結(jié)構(gòu)體包括led操作的所有信息，和回調(diào)函數(shù)

注冊struct led_classdev結(jié)構(gòu)圖變量：

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

對于gpio閃光燈，則需要填充一下結(jié)構(gòu)體：

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閃光燈注冊函數(shù)：

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

2. gpio閃光燈sgm3141驅(qū)動詳解

看上圖：

1. sgm3141驅(qū)動通過函數(shù)led_classdev_flash_register()->led_classdev_register()向led子系統(tǒng)注冊該設(shè)備
2. sgm3141驅(qū)動通過函數(shù)v4l2_async_register_subdev()向v4l2子系統(tǒng)注冊該設(shè)備
3. 如果用戶直接通過/sys/class/leds/gpio-flash/flash_strobe文件操作led燈，則會直接調(diào)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. 如果用戶的app拍照時操作閃光燈，則是通過v4l2子系統(tǒng)調(diào)用下發(fā)ioctl命令 命令序列：

V4L2_CID_FLASH_LED_MODE ：設(shè)置led mod為 V4L2_FLASH_LED_MODE_TORCH(2),并點燈V4L2_CID_FLASH_LED_MODE：到達指定超時時間（2.7秒），設(shè)置led mod為 V4L2_FLASH_LED_MODE_NONE 0V4L2_CID_FLASH_LED_MODE：在此設(shè)置led mod為V4L2_FLASH_LED_MODE_FLASH(1)V4L2_CID_FLASH_STROBE_STOP:停止閃光

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驅(qū)動注冊流程分析 驅(qū)動架構(gòu)基于platform總線，platform_driver 結(jié)構(gòu)體如下：

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, },};