Documentation/leds/leds-class-flash.txt

   1
   2 Flash LED handling under Linux
   3 ==============================
   4
   5 Some LED devices provide two modes - torch and flash. In the LED subsystem
   6 those modes are supported by LED class (see Documentation/leds/leds-class.txt)
   7 and LED Flash class respectively. The torch mode related features are enabled
   8 by default and the flash ones only if a driver declares it by setting
   9 LED_DEV_CAP_FLASH flag.
  10
  11 In order to enable the support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol
  12 must be defined in the kernel config. A LED Flash class driver must be
  13 registered in the LED subsystem with led_classdev_flash_register function.
  14
  15 Following 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
  25 V4L2 flash wrapper for flash LEDs
  26 =================================
  27
  28 A LED subsystem driver can be controlled also from the level of VideoForLinux2
  29 subsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to
  30 be defined in the kernel config.
  31
  32 The driver must call the v4l2_flash_init function to get registered in the
  33 V4L2 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
  60 On remove the v4l2_flash_release function has to be called, which takes one
  61 argument - struct v4l2_flash pointer returned previously by v4l2_flash_init.
  62 This function can be safely called with NULL or error pointer argument.
  63
  64 Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the
  65 v4l2 flash wrapper.
  66
  67 Once the V4L2 sub-device is registered by the driver which created the Media
  68 controller device, the sub-device node acts just as a node of a native V4L2
  69 flash API device would. The calls are simply routed to the LED flash API.
  70
  71 Opening the V4L2 flash sub-device makes the LED subsystem sysfs interface
  72 unavailable. The interface is re-enabled after the V4L2 flash sub-device
  73 is closed.