Documentation: leds: Add description of v4l2-flash sub-device

This patch extends LED Flash class documention by
the description of interactions with v4l2-flash sub-device.

Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

diff --git a/Documentation/leds/leds-class-flash.txt b/Documentation/leds/leds-class-flash.txt
index 19bb67355424a053127f19b12f347a9cdafd513a..8da3c6f4b60b8d095056f98a5da495d6d971931e 100644 (file)
--- a/Documentation/leds/leds-class-flash.txt
+++ b/Documentation/leds/leds-class-flash.txt
@@ -20,3 +20,54 @@ Following sysfs attributes are exposed for controlling flash LED devices:
        - 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.