leds: flash: document sysfs interface

Add a documentation of LED Flash class specific sysfs attributes.
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

Documentation/ABI/testing/sysfs-class-led-flash

+What:		/sys/class/leds/<led>/flash_brightness
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read/write
+		Set the brightness of this LED in the flash strobe mode, in
+		microamperes. The file is created only for the flash LED devices
+		that support setting flash brightness.
+
+		The value is between 0 and
+		/sys/class/leds/<led>/max_flash_brightness.
+
+What:		/sys/class/leds/<led>/max_flash_brightness
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read only
+		Maximum brightness level for this LED in the flash strobe mode,
+		in microamperes.
+
+What:		/sys/class/leds/<led>/flash_timeout
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read/write
+		Hardware timeout for flash, in microseconds. The flash strobe
+		is stopped after this period of time has passed from the start
+		of the strobe. The file is created only for the flash LED
+		devices that support setting flash timeout.
+
+What:		/sys/class/leds/<led>/max_flash_timeout
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read only
+		Maximum flash timeout for this LED, in microseconds.
+
+What:		/sys/class/leds/<led>/flash_strobe
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read/write
+		Flash strobe state. When written with 1 it triggers flash strobe
+		and when written with 0 it turns the flash off.
+
+		On read 1 means that flash is currently strobing and 0 means
+		that flash is off.
+
+What:		/sys/class/leds/<led>/flash_fault
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read only
+		Space separated list of flash faults that may have occurred.
+		Flash faults are re-read after strobing the flash. Possible
+		flash faults:
+
+		* led-over-voltage - flash controller voltage to the flash LED
+			has exceeded the limit specific to the flash controller
+		* flash-timeout-exceeded - the flash strobe was still on when
+			the timeout set by the user has expired; not all flash
+			controllers may set this in all such conditions
+		* controller-over-temperature - the flash controller has
+			overheated
+		* controller-short-circuit - the short circuit protection
+			of the flash controller has been triggered
+		* led-power-supply-over-current - current in the LED power
+			supply has exceeded the limit specific to the flash
+			controller
+		* indicator-led-fault - the flash controller has detected
+			a short or open circuit condition on the indicator LED
+		* led-under-voltage - flash controller voltage to the flash
+			LED has been below the minimum limit specific to
+			the flash
+		* controller-under-voltage - the input voltage of the flash
+			controller is below the limit under which strobing the
+			flash at full current will not be possible;
+			the condition persists until this flag is no longer set
+		* led-over-temperature - the temperature of the LED has exceeded
+			its allowed upper limit