[PATCH v4 09/12] Documentation: leds: Add description of v4l2-flash sub-device

[Jacek Anaszewski <j.anaszewski@samsung.com>]

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: Bryan Wu <cooloney@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
---
 Documentation/leds/leds-class-flash.txt |   47 +++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/Documentation/leds/leds-class-flash.txt b/Documentation/leds/leds-class-flash.txt
index 19bb673..ad80eeb 100644
--- a/Documentation/leds/leds-class-flash.txt
+++ b/Documentation/leds/leds-class-flash.txt
@@ -20,3 +20,50 @@ 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 three arguments:
+- fled_cdev : the LED Flash class device to wrap
+- 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>,
+	* intensity - constraints for the LED in the TORCH or INDICATOR mode,
+		in microamperes,
+	* has_external_strobe - determines whether the flash strobe source
+		can be switched to external,
+	* indicator_led - signifies that a led is of indicator type, which
+		implies that it can have only two V4L2 controls:
+		V4L2_CID_FLASH_INDICATOR_INTENSITY and V4L2_CID_FLASH_FAULT.
+
+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.
+
+Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the
+v4l2-flash API.
+
+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.
-- 
1.7.9.5