linux-kernel - Re: [PATCH v5 1/4] leds: core: add generic support for RGB Color LED's

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Date:	Mon, 4 Apr 2016 23:34:10 +0200
From:	Jacek Anaszewski <jacek.anaszewski@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Jacek Anaszewski <j.anaszewski@...sung.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Greg KH <greg@...ah.com>, linux-leds@...r.kernel.org,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	pali.rohar@...il.com, sre@...nel.org, khilman@...nel.org,
	aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
	Patrik Bachan <patrikbachan@...il.com>, serge@...lyn.com
Subject: Re: [PATCH v5 1/4] leds: core: add generic support for RGB Color
 LED's

Hi Pavel,

On 04/01/2016 11:18 PM, Pavel Machek wrote:
> Hi!
>
>>>> It would have the same downsides as in case of having r, g and b in
>>>> separate attributes, i.e. - problems with setting LED colour in
>>>> a consistent way. This way LED blinking in whatever colour couldn't
>>>> be supported reliably. It was one of your primary rationale standing
>>>> behind this design, if I remember correctly. Second - what about
>>>> triggers? We've had a long discussion about it and this design turned
>>>> out to be most fitting.
>>>
>>> Are on/off triggers really that useful for a LED that can produce 16
>>> million colors?
>>>
>>> I believe we should support patterns for RGB LEDs. Something like
>>> [ (time, r, g, b), ... ] . Ok, what about this one?
>>>
>>> Lets say we have
>>>
>>> /sys/class/pattern/lp5533::0
>>> /sys/class/pattern/software::0
>>>
>>> /sys/class/led/n900::red ; default trigger "lp5533::0:0"
>>> /sys/class/led/n900::green ; default trigger "lp5533::0:1"
>>> /sys/class/led/n900::blue ; default trigger "lp5533::0:2"
>>>
>>> Normally, pattern would correspond to one RGB LED. We could have
>>> attribute "/sys/class/pattern/lp5533::0/color" containing R,G,B for
>>> this pattern.

Could you give an example on how to set a color for RGB LED using
this interface? Would it be compatible with LED triggers?
Where the "pattern" class would be implemented?

>> This involves the same issue you were opposed to: three values per
>> sysfs attribute.
>
> And solves a lot of other things. Like actually being backwards
> compatible.
>
> And yes, it involves three values in a file, but now it is array of
> led brightnesses, and that might actually be acceptable. (At least the
> values have uniform meaning).
 >
> Plus, it is not "issue you were opposed to" it is "something that is
> not permitted by sysfs maintainers".

-- 
Best regards,
Jacek Anaszewski