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Commit aaf2cbca authored by Jacek Anaszewski's avatar Jacek Anaszewski Committed by Bryan Wu
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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: default avatarJacek Anaszewski <j.anaszewski@samsung.com>
Acked-by: default avatarKyungmin Park <kyungmin.park@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Acked-by: default avatarSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: default avatarBryan Wu <cooloney@gmail.com>
parent 589fca16

Documentation/leds/leds-class-flash.txt

+51 −0
Original line number Diff line number Diff line
@@ -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.