1*4882a593Smuzhiyun============================== 2*4882a593SmuzhiyunFlash LED handling under Linux 3*4882a593Smuzhiyun============================== 4*4882a593Smuzhiyun 5*4882a593SmuzhiyunSome LED devices provide two modes - torch and flash. In the LED subsystem 6*4882a593Smuzhiyunthose modes are supported by LED class (see Documentation/leds/leds-class.rst) 7*4882a593Smuzhiyunand LED Flash class respectively. The torch mode related features are enabled 8*4882a593Smuzhiyunby default and the flash ones only if a driver declares it by setting 9*4882a593SmuzhiyunLED_DEV_CAP_FLASH flag. 10*4882a593Smuzhiyun 11*4882a593SmuzhiyunIn order to enable the support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol 12*4882a593Smuzhiyunmust be defined in the kernel config. A LED Flash class driver must be 13*4882a593Smuzhiyunregistered in the LED subsystem with led_classdev_flash_register function. 14*4882a593Smuzhiyun 15*4882a593SmuzhiyunFollowing sysfs attributes are exposed for controlling flash LED devices: 16*4882a593Smuzhiyun(see Documentation/ABI/testing/sysfs-class-led-flash) 17*4882a593Smuzhiyun 18*4882a593Smuzhiyun - flash_brightness 19*4882a593Smuzhiyun - max_flash_brightness 20*4882a593Smuzhiyun - flash_timeout 21*4882a593Smuzhiyun - max_flash_timeout 22*4882a593Smuzhiyun - flash_strobe 23*4882a593Smuzhiyun - flash_fault 24*4882a593Smuzhiyun 25*4882a593Smuzhiyun 26*4882a593SmuzhiyunV4L2 flash wrapper for flash LEDs 27*4882a593Smuzhiyun================================= 28*4882a593Smuzhiyun 29*4882a593SmuzhiyunA LED subsystem driver can be controlled also from the level of VideoForLinux2 30*4882a593Smuzhiyunsubsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to 31*4882a593Smuzhiyunbe defined in the kernel config. 32*4882a593Smuzhiyun 33*4882a593SmuzhiyunThe driver must call the v4l2_flash_init function to get registered in the 34*4882a593SmuzhiyunV4L2 subsystem. The function takes six arguments: 35*4882a593Smuzhiyun 36*4882a593Smuzhiyun- dev: 37*4882a593Smuzhiyun flash device, e.g. an I2C device 38*4882a593Smuzhiyun- of_node: 39*4882a593Smuzhiyun of_node of the LED, may be NULL if the same as device's 40*4882a593Smuzhiyun- fled_cdev: 41*4882a593Smuzhiyun LED flash class device to wrap 42*4882a593Smuzhiyun- iled_cdev: 43*4882a593Smuzhiyun LED flash class device representing indicator LED associated with 44*4882a593Smuzhiyun fled_cdev, may be NULL 45*4882a593Smuzhiyun- ops: 46*4882a593Smuzhiyun V4L2 specific ops 47*4882a593Smuzhiyun 48*4882a593Smuzhiyun * external_strobe_set 49*4882a593Smuzhiyun defines the source of the flash LED strobe - 50*4882a593Smuzhiyun V4L2_CID_FLASH_STROBE control or external source, typically 51*4882a593Smuzhiyun a sensor, which makes it possible to synchronise the flash 52*4882a593Smuzhiyun strobe start with exposure start, 53*4882a593Smuzhiyun * intensity_to_led_brightness and led_brightness_to_intensity 54*4882a593Smuzhiyun perform 55*4882a593Smuzhiyun enum led_brightness <-> V4L2 intensity conversion in a device 56*4882a593Smuzhiyun specific manner - they can be used for devices with non-linear 57*4882a593Smuzhiyun LED current scale. 58*4882a593Smuzhiyun- config: 59*4882a593Smuzhiyun configuration for V4L2 Flash sub-device 60*4882a593Smuzhiyun 61*4882a593Smuzhiyun * dev_name 62*4882a593Smuzhiyun the name of the media entity, unique in the system, 63*4882a593Smuzhiyun * flash_faults 64*4882a593Smuzhiyun bitmask of flash faults that the LED flash class 65*4882a593Smuzhiyun device can report; corresponding LED_FAULT* bit definitions are 66*4882a593Smuzhiyun available in <linux/led-class-flash.h>, 67*4882a593Smuzhiyun * torch_intensity 68*4882a593Smuzhiyun constraints for the LED in TORCH mode 69*4882a593Smuzhiyun in microamperes, 70*4882a593Smuzhiyun * indicator_intensity 71*4882a593Smuzhiyun constraints for the indicator LED 72*4882a593Smuzhiyun in microamperes, 73*4882a593Smuzhiyun * has_external_strobe 74*4882a593Smuzhiyun determines whether the flash strobe source 75*4882a593Smuzhiyun can be switched to external, 76*4882a593Smuzhiyun 77*4882a593SmuzhiyunOn remove the v4l2_flash_release function has to be called, which takes one 78*4882a593Smuzhiyunargument - struct v4l2_flash pointer returned previously by v4l2_flash_init. 79*4882a593SmuzhiyunThis function can be safely called with NULL or error pointer argument. 80*4882a593Smuzhiyun 81*4882a593SmuzhiyunPlease refer to drivers/leds/leds-max77693.c for an exemplary usage of the 82*4882a593Smuzhiyunv4l2 flash wrapper. 83*4882a593Smuzhiyun 84*4882a593SmuzhiyunOnce the V4L2 sub-device is registered by the driver which created the Media 85*4882a593Smuzhiyuncontroller device, the sub-device node acts just as a node of a native V4L2 86*4882a593Smuzhiyunflash API device would. The calls are simply routed to the LED flash API. 87*4882a593Smuzhiyun 88*4882a593SmuzhiyunOpening the V4L2 flash sub-device makes the LED subsystem sysfs interface 89*4882a593Smuzhiyununavailable. The interface is re-enabled after the V4L2 flash sub-device 90*4882a593Smuzhiyunis closed. 91