1 2Flash LED handling under Linux 3============================== 4 5Some LED devices provide two modes - torch and flash. In the LED subsystem 6those modes are supported by LED class (see Documentation/leds/leds-class.txt) 7and LED Flash class respectively. The torch mode related features are enabled 8by default and the flash ones only if a driver declares it by setting 9LED_DEV_CAP_FLASH flag. 10 11In order to enable the support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol 12must be defined in the kernel config. A LED Flash class driver must be 13registered in the LED subsystem with led_classdev_flash_register function. 14 15Following sysfs attributes are exposed for controlling flash LED devices: 16(see Documentation/ABI/testing/sysfs-class-led-flash) 17 - flash_brightness 18 - max_flash_brightness 19 - flash_timeout 20 - max_flash_timeout 21 - flash_strobe 22 - flash_fault 23 24 25V4L2 flash wrapper for flash LEDs 26================================= 27 28A LED subsystem driver can be controlled also from the level of VideoForLinux2 29subsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to 30be defined in the kernel config. 31 32The driver must call the v4l2_flash_init function to get registered in the 33V4L2 subsystem. The function takes six arguments: 34- dev : flash device, e.g. an I2C device 35- of_node : of_node of the LED, may be NULL if the same as device's 36- fled_cdev : LED flash class device to wrap 37- iled_cdev : LED flash class device representing indicator LED associated with 38 fled_cdev, may be NULL 39- ops : V4L2 specific ops 40 * external_strobe_set - defines the source of the flash LED strobe - 41 V4L2_CID_FLASH_STROBE control or external source, typically 42 a sensor, which makes it possible to synchronise the flash 43 strobe start with exposure start, 44 * intensity_to_led_brightness and led_brightness_to_intensity - perform 45 enum led_brightness <-> V4L2 intensity conversion in a device 46 specific manner - they can be used for devices with non-linear 47 LED current scale. 48- config : configuration for V4L2 Flash sub-device 49 * dev_name - the name of the media entity, unique in the system, 50 * flash_faults - bitmask of flash faults that the LED flash class 51 device can report; corresponding LED_FAULT* bit definitions are 52 available in <linux/led-class-flash.h>, 53 * torch_intensity - constraints for the LED in TORCH mode 54 in microamperes, 55 * indicator_intensity - constraints for the indicator LED 56 in microamperes, 57 * has_external_strobe - determines whether the flash strobe source 58 can be switched to external, 59 60On remove the v4l2_flash_release function has to be called, which takes one 61argument - struct v4l2_flash pointer returned previously by v4l2_flash_init. 62This function can be safely called with NULL or error pointer argument. 63 64Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the 65v4l2 flash wrapper. 66 67Once the V4L2 sub-device is registered by the driver which created the Media 68controller device, the sub-device node acts just as a node of a native V4L2 69flash API device would. The calls are simply routed to the LED flash API. 70 71Opening the V4L2 flash sub-device makes the LED subsystem sysfs interface 72unavailable. The interface is re-enabled after the V4L2 flash sub-device 73is closed. 74