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Message-ID: <f4a9e090-3712-200e-bd09-70090c9cccbc@collabora.com>
Date:   Mon, 29 May 2023 10:02:28 +0200
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Subject: Re: [PATCH] arm64: dts: mediatek: mt8173-elm: remove panel model
 number in DT
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To:     Doug Anderson <dianders@chromium.org>,
        Icenowy Zheng <uwu@icenowy.me>,
        Pin-yen Lin <treapking@chromium.org>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, dri-devel@lists.freedesktop.org
References: <20230526100801.16310-1-uwu@icenowy.me>
 <CAD=FV=UxrFVZXn+dtgamttTVopWMSVbxYsHCGG_tS+3OTXbHiw@mail.gmail.com>
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
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Il 26/05/23 16:24, Doug Anderson ha scritto:
> Hi,
> 
> On Fri, May 26, 2023 at 3:09 AM Icenowy Zheng <uwu@icenowy.me> wrote:
>>
>> Currently a specific panel number is used in the Elm DTSI, which is
>> corresponded to a 12" panel. However, according to the official Chrome
>> OS devices document, Elm refers to Acer Chromebook R13, which, as the
>> name specifies, uses a 13.3" panel, which comes with EDID information.
>>
>> As the kernel currently prioritizes the hardcoded timing parameters
>> matched with the panel number compatible, a wrong timing will be applied
>> to the 13.3" panel on Acer Chromebook R13, which leads to blank display.
>>
>> Because the Elm DTSI is shared with Hana board, and Hana corresponds to
>> multiple devices from 11" to 14", a certain panel model number shouldn't
>> be present, and driving the panel according to its EDID information is
>> necessary.
>>
>> Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
>> ---
>>   arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> We went through a bunch of back-and-forth here but in the end in the
> ChromeOS tree we have "edp-panel" as the "compatible" here in the
> ChromeOS 5.15 tree and this makes sense.
> 
> Reviewed-by: Douglas Anderson <dianders@chromium.org>
> 
> ...in theory one would wish for a "Fixes" tag, but I think in previous
> discussions it was decided that it was too complicated. Hardcoding the
> other compatible string has always been technically wrong, but I guess
> it worked at some point in time. The more correct way (as you're doing
> here) needs the DP AUX bus support and the generic eDP panels, both of
> which are significantly newer than the elm dts. So I guess leaving no
> "Fixes" tag is OK, or perhaps you could do the somewhat weak:
> 
> Fixes: c2d94f72140a ("arm64: dts: mediatek: mt8173-elm: Move display
> to ps8640 auxiliary bus")

I remember I didn't change the compatible to panel-edp because it didn't
work at that time, but it does now... I'm not sure what actually fixed that
and if the commit(s) was/were backported to that suggested point, so I
would leave the Fixes tag out, as that may break older kernels.

Anyway, for this commit:

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>