linux-kernel - Re: [PATCH 09/10] backlight: qcom-wled: Consistently use enabled-strings in set

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Date:   Tue, 5 Oct 2021 12:12:30 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     phone-devel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Pavel Dubrova <pashadubrova@...il.com>,
        Kiran Gunda <kgunda@...eaurora.org>,
        Courtney Cavin <courtney.cavin@...ymobile.com>,
        Bryan Wu <cooloney@...il.com>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/10] backlight: qcom-wled: Consistently use
 enabled-strings in set_brightness

On 2021-10-05 10:33:31, Daniel Thompson wrote:
> On Mon, Oct 04, 2021 at 09:27:40PM +0200, Marijn Suijten wrote:
> > The hardware is capable of controlling any non-contiguous sequence of
> > LEDs specified in the DT using qcom,enabled-strings as u32
> > array, and this also follows from the DT-bindings documentation.  The
> > numbers specified in this array represent indices of the LED strings
> > that are to be enabled and disabled.
> > 
> > Its value is appropriately used to setup and enable string modules, but
> > completely disregarded in the set_brightness paths which only iterate
> > over the number of strings linearly.
> > Take an example where only string 2 is enabled with
> > qcom,enabled_strings=<2>: this string is appropriately enabled but
> > subsequent brightness changes would have only touched the zero'th
> > brightness register because num_strings is 1 here.  This is simply
> > addressed by looking up the string for this index in the enabled_strings
> > array just like the other codepaths that iterate over num_strings.
> 
> This isn't true until patch 10 is applied!

Patch 9 and 10 were split up at a last resort to prevent a clash in the
title, apologies for that.

> Given both patches fix the same issue in different functions I'd prefer
> these to be squashed together (and doubly so because the autodetect code
> uses set_brightness() as a helper function).

That's a fair reason, and solution I agree on.  I'll figure out how to
generify the title and re-spin this patchset except if there are other
reviewers/maintainers I should wait for.

- Marijn

> Daniel.