linux-kernel - Re: [PATCH] arm64: dts: mediatek: mt8173-elm: remove panel model number in DT

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Date:   Tue, 30 May 2023 13:03:39 +0800
From:   Icenowy Zheng <uwu@...nowy.me>
To:     Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Doug Anderson <dianders@...omium.org>,
        Pin-yen Lin <treapking@...omium.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] arm64: dts: mediatek: mt8173-elm: remove panel model
 number in DT

在 2023-05-29星期一的 18:28 +0200，Matthias Brugger写道：
> 
> 
> On 29/05/2023 10:45, Icenowy Zheng wrote:
> > 在 2023-05-29星期一的 10:02 +0200，AngeloGioacchino Del Regno写道：
> > > Il 26/05/23 16:24, Doug Anderson ha scritto:
> > > > Hi,
> > > > 
> > > > On Fri, May 26, 2023 at 3:09 AM Icenowy Zheng <uwu@...nowy.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@...nowy.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@...omium.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 kernel.
> > 
> > Well at least I developed this patch on v6.3.
> > 
> > (In fact the same kernel config do not boot to system at all on
> > v6.0/v6.1 when I do make olddefconfig then build)
> > 
> 
> I applied the patch without the fixes tag. Lets stay on the secure
> side to not 
> break older kernels.

Well I think this patch is at least meaningful to get backported to
v6.3.

Should we cc stable@...r.kernel.org ?

> 
> Regards,
> Matthias
> 
> > > 
> > > Anyway, for this commit:
> > > 
> > > Reviewed-by: AngeloGioacchino Del Regno
> > > <angelogioacchino.delregno@...labora.com>
> >