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- 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
- LED_DEV_CAP_FLASH flag.
- 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:
- (see Documentation/ABI/testing/sysfs-class-led-flash)
- - 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
- is closed.
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