linux-kernel - Re: [RESEND PATCH v2 09/13] backlight: qcom-wled: Respect enabled-strings in set

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Date:   Fri, 12 Nov 2021 12:20:01 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>
Cc:     phone-devel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.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>,
        Bryan Wu <cooloney@...il.com>, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org
Subject: Re: [RESEND PATCH v2 09/13] backlight: qcom-wled: Respect
 enabled-strings in set_brightness

On Fri, Nov 12, 2021 at 01:27:02AM +0100, 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.
> 
> Likewise enabled_strings is now also used in the autodetection path for
> consistent behaviour: when a list of strings is specified in DT only
> those strings will be probed for autodetection, analogous to how the
> number of strings that need to be probed is already bound by
> qcom,num-strings.  After all autodetection uses the set_brightness
> helpers to set an initial value, which could otherwise end up changing
> brightness on a different set of strings.
> 
> Fixes: 775d2ffb4af6 ("backlight: qcom-wled: Restructure the driver for WLED3")
> Fixes: 03b2b5e86986 ("backlight: qcom-wled: Add support for WLED4 peripheral")
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>

Reviewed-by: Daniel Thompson <daniel.thompson@...aro.org>


Daniel.