linux-kernel - Re: [PATCH v8 1/2] leds: core: Introduce LED pattern trigger

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Message-ID: <0190dc10-99a3-abb7-b196-a537c49a2b6e@gmail.com>
Date:   Sat, 8 Sep 2018 22:19:11 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Baolin Wang <baolin.wang@...aro.org>
Cc:     pavel@....cz, rteysseyre@...il.com, broonie@...nel.org,
        linus.walleij@...aro.org, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 1/2] leds: core: Introduce LED pattern trigger

Hi Bjorn,

On 09/08/2018 07:02 AM, Bjorn Andersson wrote:
> On Tue 04 Sep 04:01 PDT 2018, Baolin Wang wrote:
> 
>> diff --git a/Documentation/ABI/testing/sysfs-class-led-trigger-pattern b/Documentation/ABI/testing/sysfs-class-led-trigger-pattern
> [..]
>> +What:		/sys/class/leds/<led>/hw_pattern
>> +Date:		September 2018
>> +KernelVersion:	4.20
>> +Description:
>> +		Specify a hardware pattern for the LED, for LED hardware that
>> +		supports autonomously controlling brightness over time, according
>> +		to some preprogrammed hardware patterns.
>> +
>> +		Since different LED hardware can have different semantics of
>> +		hardware patterns, each driver is expected to provide its own
>> +		description for the hardware patterns in their ABI documentation
>> +		file.
>> +
> 
> So, after a full circle we're back at drivers with support for hardware
> patterns should have their own ABI for setting that pattern.
> 
> The controls for my hardware is:
> * a list of brightness values
> * the rate of the pattern
> * a flag to indicate that the pattern should be played from start
>   to end, end to start or start to end to start
> * a boolean indicating if the pattern should be played once or repeated
>   indefinitely.
> 
> Given that the interface now is hw specific, what benefit is there to
> attempt to cram these 4 knobs into "hw_pattern"? Or am I allowed to
> create additional files for the latter three?

So this is an argument corroborating my concerns raised in [0].
I really think that we should allow for custom pattern interfaces
defined by LED class drivers.

>> +What:		/sys/class/leds/<led>/repeat
>> +Date:		September 2018
>> +KernelVersion:	4.20
>> +Description:
>> +		Specify a pattern repeat number. 0 means repeat indefinitely.
>> +
>> +		This file will always return the originally written repeat
>> +		number.
> 
> I'm still convinced that this will confuse our users and to me it would
> be more logical if this denotes the number of times the pattern should
> be repeated, with e.g. negative numbers denoting infinite.

Sounds reasonable. Let's change this semantics as you propose.

> In particular I expect to have to explain why my driver expects that you
> write 0 in the file named "repeat" to make it repeat and 1 to make it
> not repeat.



[0] https://lkml.org/lkml/2018/9/3/1192

-- 
Best regards,
Jacek Anaszewski