linux-kernel - Re: [PATCH v3 1/2] leds: core: Introduce generic pattern interface

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Date:   Wed, 18 Jul 2018 17:13:41 -0500
From:   David Lechner <david@...hnology.com>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>
Cc:     Baolin Wang <baolin.wang@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] leds: core: Introduce generic pattern interface

On 07/18/2018 02:22 PM, Jacek Anaszewski wrote:
> On 07/18/2018 08:54 PM, Jacek Anaszewski wrote:
>> On 07/18/2018 09:56 AM, Pavel Machek wrote:
>>> Hi!
>>>
>>>>>>>> I believe I meant "changing patterns from kernel in response to events
>>>>>>>> is probably overkill"... or something like that.
>>>>>>>
>>>>>>> Anyway -- to clean up the confusion -- I'd like to see
>>>>>>>
>>>>>>> echo pattern > trigger
>>>>>>> echo "1 2 3 4 5 6 7 8" > somewhere
>>>>>>
>>>>>> s/somewhere/pattern/
>>>>>>
>>>>>> pattern trigger should create "pattern" file similarly how ledtrig-timer
>>>>>> creates delay_{on|off} files.
>>>
>>> Yes, that sounds reasonable. v5 still says
>>>
>>> +               Writing non-empty string to this file will activate the pattern,
>>> +               and empty string will disable the pattern.
>>>
>>> I'd deactivate the pattern by simply writing something else to the
>>> trigger file.
>>
>> Please keep in mind that this is ABI documentation for the pattern file
>> to be exposed by LED core, and not by the pattern trigger, that, as we
>> agreed, will be implemented later. In this case, I'd go for
> 
> Gosh, I got completely distracted by the recent discussion about
> pattern synchronization.
> 
> So, to recap, we need to decide if we are taking Baolin's solution
> or we're opting for implementing pattern trigger.

I think we should take Baolin's solution.

> 
> If we choose the latter, then we will also need some software
> pattern engine in the trigger, to be applied as a software pattern
> fallback for the devices without hardware pattern support.
> It will certainly delay the contribution process, provided that Baolin
> would find time for this work at all.
> 
> I'd just take v5 based solution for now (with improved semantics
> of disabling pattern - in this case my reasoning from the message
> I'm replying to is still valid),
> 
>> "echo 0 > brightness" as a command disabling pattern. The same operation
>> disables triggers, so later transition to using pattern trigger will be
>> seamless for userspace.
>>
>