linux-kernel - Re: [PATCH/RFC v9 02/19] Documentation: leds: Add description of LED Flash class extension

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Message-id: <54802C9F.8030101@samsung.com>
Date:	Thu, 04 Dec 2014 10:42:55 +0100
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Sakari Ailus <sakari.ailus@....fi>
Cc:	linux-leds@...r.kernel.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, kyungmin.park@...sung.com,
	b.zolnierkie@...sung.com, pavel@....cz, cooloney@...il.com,
	rpurdie@...ys.net, s.nawrocki@...sung.com, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org
Subject: Re: [PATCH/RFC v9 02/19] Documentation: leds: Add description of LED
 Flash class extension

Hi Sakari,

Thanks for the review.

On 12/03/2014 06:08 PM, Sakari Ailus wrote:
> Hi Jacek,
>
> On Wed, Dec 03, 2014 at 05:06:37PM +0100, Jacek Anaszewski wrote:
>> The documentation being added contains overall description of the
>> LED Flash Class and the related sysfs attributes.
>>
>> Signed-off-by: Jacek Anaszewski <j.anaszewski@...sung.com>
>> Acked-by: Kyungmin Park <kyungmin.park@...sung.com>
>> Cc: Bryan Wu <cooloney@...il.com>
>> Cc: Richard Purdie <rpurdie@...ys.net>
>> ---
>>   Documentation/leds/leds-class-flash.txt |   50 +++++++++++++++++++++++++++++++
>>   1 file changed, 50 insertions(+)
>>   create mode 100644 Documentation/leds/leds-class-flash.txt
>>
>> diff --git a/Documentation/leds/leds-class-flash.txt b/Documentation/leds/leds-class-flash.txt
>> new file mode 100644
>> index 0000000..82e58b1
>> --- /dev/null
>> +++ b/Documentation/leds/leds-class-flash.txt
>> @@ -0,0 +1,50 @@
>> +
>> +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)
>> +	- 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
>
> s/atrribute/attribute/
>
>> +			      the flash led will be strobed synchronously
>> +			      with the other one controlled by the same
>> +			      device; flash timeout setting is inherited
>> +			      from the led being strobed explicitly and
>> +			      flash brightness setting of a sub-led's
>> +			      being synchronized is used (RW)
>
> The flash brightness shouldn't be determined by the strobed LED. If this is
> a property of the hardware, then be it, but in general no, it it shouldn't
> be an interface requirement. I think this should just say that the strobe is
> synchronised.

I intended this to sound exactly as you laid it out above, but maybe it
is obscure English. "and flash brightness setting of a sub-led >>>being
synchronized<<< is used" - from my point of view the led being
synchronized is the one that isn't strobed explicitly. But I'm ok with
confining ourselves only to saying that strobe is synchronized.

> How does the user btw. figure out which flash LEDs may be strobed
> synchronously using the LED flash interface?

The flash_sync_strobe argument is absent if synchronized strobe
is not available for a LED. The driver defines this by setting
newly added LED_DEV_CAP_COMPOUND flag.

Best Regards,
Jacek Anaszewski
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