linux-kernel - Re: [PATCH v5 1/2] leds: core: Introduce LED pattern trigger

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Message-ID: <20180824201227.GB17146@amd>
Date:   Fri, 24 Aug 2018 22:12:27 +0200
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Baolin Wang <baolin.wang@...aro.org>, rteysseyre@...il.com,
        bjorn.andersson@...aro.org, broonie@...nel.org,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/2] leds: core: Introduce LED pattern trigger

On Fri 2018-08-24 21:49:50, Jacek Anaszewski wrote:
> Hi Pavel,
> 
> On 08/24/2018 12:11 PM, Pavel Machek wrote:
> > Hi!
> > 
> >> I think that it would be more flexible if software pattern fallback
> >> was applied in case of pattern_set failure. Otherwise, it would
> >> lead to the situation where LED class devices that support hardware
> >> blinking couldn't be applied the same set of patterns as LED class
> >> devices that don't implement pattern_set. The latter will always have to
> >> resort to using software pattern engine which will accept far greater
> >> amount of pattern combinations.
> >>
> >> In this case we need to discuss on what basis the decision will be
> >> made on whether hardware or software engine will be used.
> >>
> >> Possible options coming to mind:
> >> - an interface will be provided to determine max difference between
> >>   the settings supported by the hardware and the settings requested by
> >>   the user, that will result in aligning user's setting to the hardware
> >>   capabilities
> >> - the above alignment rate will be predefined instead
> >> - hardware engine will be used only if user requests supported settings
> >>   on the whole span of the requested pattern
> >> - in each of the above cases it would be worth to think of the
> >>   interface to show the scope of the settings supported by hardware
> > 
> > I'd recommend keeping it simple. We use hardware engine if driver
> > author thinks pattern is "close enough".
> 
> The thing is that in the ledtrig-pattern v5 implementation there
> is no option of using software fallback if pattern_set op
> is initialized:
> 
> +	if (led_cdev->pattern_set) {
> +		return led_cdev->pattern_set(led_cdev, data->patterns,
> +					     data->npatterns, data->repeat);
> +	}

Yeah, that sounds wrong. (Sorry I did not pay enough attention).

It pattern_set() returns special error code, it should just continue
and use software pattern fallback.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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