|Flash LED handling under Linux
|Some LED devices provide two modes - torch and flash. In the LED subsystem
|those modes are supported by LED class (see Documentation/leds/leds-class.txt)
|and LED Flash class respectively. The torch mode related features are enabled
|by default and the flash ones only if a driver declares it by setting
|In order to enable the support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol
|must be defined in the kernel config. A LED Flash class driver must be
|registered in the LED subsystem with led_classdev_flash_register function.
|Following sysfs attributes are exposed for controlling flash LED devices:
| - flash_brightness
| - max_flash_brightness
| - flash_timeout
| - max_flash_timeout
| - flash_strobe
| - flash_fault
|V4L2 flash wrapper for flash LEDs
|A LED subsystem driver can be controlled also from the level of VideoForLinux2
|subsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to
|be defined in the kernel config.
|The driver must call the v4l2_flash_init function to get registered in the
|V4L2 subsystem. The function takes six arguments:
|- dev : flash device, e.g. an I2C device
|- of_node : of_node of the LED, may be NULL if the same as device's
|- fled_cdev : LED flash class device to wrap
|- iled_cdev : LED flash class device representing indicator LED associated with
| fled_cdev, may be NULL
|- ops : V4L2 specific ops
| * external_strobe_set - defines the source of the flash LED strobe -
| V4L2_CID_FLASH_STROBE control or external source, typically
| a sensor, which makes it possible to synchronise the flash
| strobe start with exposure start,
| * intensity_to_led_brightness and led_brightness_to_intensity - perform
| enum led_brightness <-> V4L2 intensity conversion in a device
| specific manner - they can be used for devices with non-linear
| LED current scale.
|- config : configuration for V4L2 Flash sub-device
| * dev_name - the name of the media entity, unique in the system,
| * flash_faults - bitmask of flash faults that the LED flash class
| device can report; corresponding LED_FAULT* bit definitions are
| available in <linux/led-class-flash.h>,
| * torch_intensity - constraints for the LED in TORCH mode
| in microamperes,
| * indicator_intensity - constraints for the indicator LED
| in microamperes,
| * has_external_strobe - determines whether the flash strobe source
| can be switched to external,
|On remove the v4l2_flash_release function has to be called, which takes one
|argument - struct v4l2_flash pointer returned previously by v4l2_flash_init.
|This function can be safely called with NULL or error pointer argument.
|Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the
|v4l2 flash wrapper.
|Once the V4L2 sub-device is registered by the driver which created the Media
|controller device, the sub-device node acts just as a node of a native V4L2
|flash API device would. The calls are simply routed to the LED flash API.
|Opening the V4L2 flash sub-device makes the LED subsystem sysfs interface
|unavailable. The interface is re-enabled after the V4L2 flash sub-device