91 lines · plain
1==============================2Flash LED handling under Linux3==============================4 5Some LED devices provide two modes - torch and flash. In the LED subsystem6those modes are supported by LED class (see Documentation/leds/leds-class.rst)7and LED Flash class respectively. The torch mode related features are enabled8by default and the flash ones only if a driver declares it by setting9LED_DEV_CAP_FLASH flag.10 11In order to enable the support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol12must be defined in the kernel config. A LED Flash class driver must be13registered 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 18 - flash_brightness19 - max_flash_brightness20 - flash_timeout21 - max_flash_timeout22 - flash_strobe23 - flash_fault24 25 26V4L2 flash wrapper for flash LEDs27=================================28 29A LED subsystem driver can be controlled also from the level of VideoForLinux230subsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to31be defined in the kernel config.32 33The driver must call the v4l2_flash_init function to get registered in the34V4L2 subsystem. The function takes six arguments:35 36- dev:37 flash device, e.g. an I2C device38- of_node:39 of_node of the LED, may be NULL if the same as device's40- fled_cdev:41 LED flash class device to wrap42- iled_cdev:43 LED flash class device representing indicator LED associated with44 fled_cdev, may be NULL45- ops:46 V4L2 specific ops47 48 * external_strobe_set49 defines the source of the flash LED strobe -50 V4L2_CID_FLASH_STROBE control or external source, typically51 a sensor, which makes it possible to synchronise the flash52 strobe start with exposure start,53 * intensity_to_led_brightness and led_brightness_to_intensity54 perform55 enum led_brightness <-> V4L2 intensity conversion in a device56 specific manner - they can be used for devices with non-linear57 LED current scale.58- config:59 configuration for V4L2 Flash sub-device60 61 * dev_name62 the name of the media entity, unique in the system,63 * flash_faults64 bitmask of flash faults that the LED flash class65 device can report; corresponding LED_FAULT* bit definitions are66 available in <linux/led-class-flash.h>,67 * torch_intensity68 constraints for the LED in TORCH mode69 in microamperes,70 * indicator_intensity71 constraints for the indicator LED72 in microamperes,73 * has_external_strobe74 determines whether the flash strobe source75 can be switched to external,76 77On remove the v4l2_flash_release function has to be called, which takes one78argument - struct v4l2_flash pointer returned previously by v4l2_flash_init.79This function can be safely called with NULL or error pointer argument.80 81Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the82v4l2 flash wrapper.83 84Once the V4L2 sub-device is registered by the driver which created the Media85controller device, the sub-device node acts just as a node of a native V4L286flash API device would. The calls are simply routed to the LED flash API.87 88Opening the V4L2 flash sub-device makes the LED subsystem sysfs interface89unavailable. The interface is re-enabled after the V4L2 flash sub-device90is closed.91