linux-kernel - Re: [PATCH/RFC v8 02/14] Documentation: leds: Add description of LED Flash class extension

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Message-ID: <20141129125832.GA315@amd>
Date:	Sat, 29 Nov 2014 13:58:32 +0100
From:	Pavel Machek <pavel@....cz>
To:	Jacek Anaszewski <j.anaszewski@...sung.com>
Cc:	linux-leds@...r.kernel.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, kyungmin.park@...sung.com,
	b.zolnierkie@...sung.com, cooloney@...il.com, rpurdie@...ys.net,
	sakari.ailus@....fi, s.nawrocki@...sung.com
Subject: Re: [PATCH/RFC v8 02/14] Documentation: leds: Add description of LED
 Flash class extension

Hi!

> +Flash LED handling under Linux
> +==============================
> +
> +Some LED devices support two modes - torch and flash. The modes are
> +supported by the LED class (see Documentation/leds/leds-class.txt)
> +and LED Flash class respectively.
> +
> +In order to enable support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol
> +must be defined in the kernel config. A flash LED driver must register
> +in the LED subsystem with led_classdev_flash_register to gain flash
> +capabilities.
> +
> +Following sysfs attributes are exposed for controlling flash led devices:
> +
> +	- flash_brightness - flash LED brightness in microamperes (RW)
> +	- max_flash_brightness - maximum available flash LED brightness (RO)
> +	- indicator_brightness - privacy LED brightness in microamperes (RW)
> +	- max_indicator_brightness - maximum privacy LED brightness in
> +				     microamperes (RO)
> +	- flash_timeout - flash strobe duration in microseconds (RW)
> +	- max_flash_timeout - maximum available flash strobe duration (RO)
> +	- flash_strobe - flash strobe state (RW)
> +	- flash_sync_strobe - one flash device can control more than one
> +			      sub-led; when this atrribute is set to 1
> +			      the flash led will be strobed synchronously
> +			      with the other ones controlled by the same
> +			      device (RW)

This is not really clear. Does flash_timeout or flash_brightness need
to be set, first?

Do we really want to have separate indicator brightnesses in uA?
Should we maybe reuse existing "brightness" parameter for torch and
indication, maybe adding single (RO) indicator_brightness attribute?

> +	- flash_fault - bitmask of flash faults that may have occurred,
> +			possible flags are:
> +		* 0x01 - flash controller voltage to the flash LED has exceeded
> +			 the limit specific to the flash controller
> +		* 0x02 - 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
> +		* 0x04 - the flash controller has overheated
> +		* 0x08 - the short circuit protection of the flash controller
> +			 has been triggered
> +		* 0x10 - current in the LED power supply has exceeded the limit
> +			 specific to the flash controller
> +		* 0x40 - flash controller voltage to the flash LED has been
> +			 below the minimum limit specific to the flash
> +		* 0x80 - 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
> +		* 0x100 - the temperature of the LED has exceeded its allowed
> +			  upper limit

How are faults cleared? Should it be list of strings, instead of
bitmask? We may want to add new fault modes in future...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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