一、闪光灯基本原理
工作模式
Camera flash led分flash和torch两种模式。
-
flash：
拍照时上光灯瞬间亮一下，电流比较大，目前是1000mA，最大电流不能超过led最大承受能力 -
torch：
只用于录video或者拿led当手电筒的情况，电流不能太大，
flash开启需要先从torch过渡，这样电流可以慢慢增大，减少冲击。
二、驱动移植
1. 硬件电路
sgm3141总体来说比较简单，只有两个引脚用于控制：FLASH_EN、FLASH/TORCH。
-
FLASH_EN
闪光灯使能引脚。 -
FLASH/TORCH
此处led flash和TORCH功能共用了同一个gpio。
“ 注意: 有的摄像头是通过pwm来控制闪光灯，具体问题具体分析，不要教条”
2. 设备树
瑞芯微sdk中没有专门针对sgm3141的驱动，网上搜了一大圈也没有搜到，很多闪光灯都是基于I2C接口，通过I2C来设置上光灯的工作模式，好在sdk中有类似的芯片rgb13h驱动，该驱动只有一个引脚用于闪光灯，和我们的功能很类似。
参考驱动文件：leds-rgb13h.c
sgm3141设备树节点
flash_sgm3141:flash-sgm3141 {status = "okay";compatible = "sgmicro,sgm3141";label = "gpio-flash";pinctrl-names = "default";pinctrl-0 = <&flash_led_gpios>;led-max-microamp = <20000>;flash-max-microamp = <20000>;flash-max-timeout-us = <1000000>;strobe-gpios = <&gpio3 RK_PC7 GPIO_ACTIVE_HIGH>;enable-gpios = <&gpio3 RK_PD0 GPIO_ACTIVE_HIGH>;rockchip,camera-module-index = <0>;rockchip,camera-module-facing = "back"; };ov13850: ov13850@10 {……flash-leds = <&flash_sgm3141>;……};
pinctrl设置：
&pinctrl {……flash-led {flash_led_gpios: flash-led {rockchip,pins =/* flash led enable*/<3 RK_PD0 RK_FUNC_GPIO &pcfg_pull_none>,<3 RK_PC6 RK_FUNC_GPIO &pcfg_pull_none>;};};……};@drivers/leds/Makefile
obj-y += sgm3141.o三、xml
要app支持闪光灯，还需要修改xml文件，打开该功能
@hardware/rockchip/camera/etc/camera/camera3_profiles.xml
@hardware/rockchip/camera/etc/camera/camera3_profiles_rk356x.xml<flash.info.available value="TRUE"/>
这样，打开app就可以看到上光灯的按钮。
四、拓扑结构
拓扑结构中entity
rk3568_r:/ # media-ctl -d /dev/media0 -p
……
- entity 70: m01_f_ov5648 4-0036 (1 pad, 1 link)type V4L2 subdev subtype Sensordevice node name /dev/v4l-subdev3pad0: Source[fmt:SBGGR10/2592x1944]-> "rockchip-csi2-dphy0":0 []- entity 74: m00_b_ov13850 4-0010 (1 pad, 1 link)type V4L2 subdev subtype Sensordevice node name /dev/v4l-subdev4pad0: Source[fmt:SBGGR10/4224x3136]-> "rockchip-csi2-dphy0":0 []- entity 78: m00_b_gpio-flash (0 pad, 0 link)type V4L2 subdev subtype Flashdevice node name /dev/v4l-subdev5
-
摄像头：
m00_b_ov13850、m01_f_ov5648 -
闪光灯：
m00_b_gpio-flash，v4l2子设备/dev/v4l-subdev5
第4个字母b表示后置摄像头。
五、调试
驱动会通过sysfs创建文件节点
rk3568_r:/sys/class/leds/gpio-flash # ls
brightness flash_strobe max_brightness power trigger
device flash_timeout max_flash_timeout subsystem uevent- 亮灭灯
亮灯
rk3568_r:/sys/class/leds/gpio-flash # echo 1 > brightness
echo 1 > brightness
灭灯
1|rk3568_r:/sys/class/leds/gpio-flash # echo 0 > brightness
echo 0 > brightness
操作对应函数调用关系
[ 374.302386] Call trace:
[ 374.302428] dump_backtrace+0x0/0x178
[ 374.302471] show_stack+0x14/0x20
[ 374.302518] dump_stack+0x94/0xb4
[ 374.302560] sgm3141_led_brightness_set+0x18/0x40
[ 374.302592] led_set_brightness_nopm+0x14/0x48
[ 374.302624] led_set_brightness+0x50/0x80
[ 374.302662] brightness_store+0x74/0xc8
[ 374.302691] dev_attr_store+0x18/0x28
[ 374.302728] sysfs_kf_write+0x48/0x58
[ 374.302759] kernfs_fop_write+0xf4/0x220
[ 374.302793] __vfs_write+0x34/0x158
[ 374.302810] vfs_write+0xb0/0x1d0
[ 374.302828] ksys_write+0x64/0xe0
[ 374.302860] __arm64_sys_write+0x14/0x20
[ 374.302904] el0_svc_common.constprop.0+0x64/0x178
[ 374.302947] el0_svc_handler+0x28/0x78
[ 374.302984] el0_svc+0x8/0xc
[ 425.607850] healthd: battery l=50 v=3 t=2.6 h=2 st=3 fc=100 chg=au
[ 437.663757] CPU: 3 PID: 1727 Comm: sh Not tainted 4.19.232 #326
[ 437.663869] Hardware name: Rockchip RK3568 EVB1 DDR4 V10 Board (DT)
- 闪灯
rk3568_r:/sys/class/leds/gpio-flash # echo 1 > flash_strobe
echo 1 > flash_strobe
操作对应函数调用关系
[ 492.026239] Call trace:
[ 492.026291] dump_backtrace+0x0/0x178
[ 492.026320] show_stack+0x14/0x20
[ 492.026354] dump_stack+0x94/0xb4
[ 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
[ 494.218112] CPU: 2 PID: 1727 Comm: sh Not tainted 4.19.232 #326
[ 494.218218] Hardware name: Rockchip RK3568 EVB1 DDR4 V10 Board (DT)
“ 为方便查看驱动回调函数调用顺序，可以在下面3个回调函数入口增加dump_stack()， sgm3141_led_brightness_set() sgm3141_led_flash_strobe_set() sgm3141_set_ctrl()
”
六、app 测试驱动 log分析
1. 上电加载驱动log
rk3568_r:/ # dmesg | grep sgm3141
dmesg | grep sgm3141
[ 0.853883] sgm3141-flash flash-sgm3141: driver version: 00.01.01
[ 0.853956] sgm3141-flash flash-sgm3141: Unable to get pwm device
2. 打开摄像头
打开摄像头功能，app调用ioctl命令如下：
V4L2_CID_FLASH_LED_MODE ：app 设置led mode为 V4L2_FLASH_LED_MODE_FLASH(1)
V4L2_CID_FLASH_TIMEOUT ：设置超时时间
V4L2_CID_FLASH_STROBE_STOP ：停止闪光
[ 36.213220] sgm3141 V4L2_CID_FLASH_LED_MODE 1
[ 36.213250] sgm3141_set_ctrl(),376
[ 36.213256] sgm3141_set_output(),78 0
[ 36.213265] sgm3141_led_flash_strobe_set(),166 state=1
[ 36.213281] sgm3141_set_output(),78 1[ 36.213298] sgm3141 V4L2_CID_FLASH_TIMEOUT
[ 36.213300] sgm3141_set_ctrl(),412
[ 36.213308] sgm3141_led_flash_timeout_set(),195 timeout=500000[ 36.213318] sgm3141 V4L2_CID_FLASH_STROBE_STOP 1
[ 36.213323] sgm3141_set_ctrl(),406
[ 36.213327] sgm3141_led_flash_strobe_set(),166 state=0
[ 36.213332] sgm3141_set_output(),78 0
[ 36.213461] sgm3141_timeout_work(),117
3. 拍照
拍照功能，app调用ioctl命令如下：
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
[ 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
从log可以看出，app拍照的时候，闪光灯操作是通过v4l2下发的命令，
而我们直接操作宏dev_attr_store创建的文件节点则是通过在sysfs文件节点（brightness flash_strobe）直接调用到操作函数。
4. 退出摄像头
[ 317.882459] sgm3141 V4L2_CID_FLASH_LED_MODE 0
[ 317.882522] sgm3141_set_ctrl(),376
[ 317.882532] sgm3141_set_output(),78 0
七、驱动获取
一口君修改过的驱动已经上传到gitee，获取地址：
https://gitee.com/yikoulinux/sgm3141
