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Message-ID: <6996788b112f4795d2930a6664b3152cd9a380a8.camel@icenowy.me>
Subject: Re: [PATCH] arm64: dts: mediatek: mt8173-elm: remove panel model
 number in DT
From:   Icenowy Zheng <uwu@icenowy.me>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Doug Anderson <dianders@chromium.org>,
        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
Date:   Mon, 29 May 2023 16:45:20 +0800
In-Reply-To: <f4a9e090-3712-200e-bd09-70090c9cccbc@collabora.com>
References: <20230526100801.16310-1-uwu@icenowy.me>
         <CAD=FV=UxrFVZXn+dtgamttTVopWMSVbxYsHCGG_tS+3OTXbHiw@mail.gmail.com>
         <f4a9e090-3712-200e-bd09-70090c9cccbc@collabora.com>
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=E5=9C=A8 2023-05-29=E6=98=9F=E6=9C=9F=E4=B8=80=E7=9A=84 10:02 +0200=EF=BC=
=8CAngeloGioacchino Del Regno=E5=86=99=E9=81=93=EF=BC=9A
> Il 26/05/23 16:24, Doug Anderson ha scritto:
> > Hi,
> >=20
> > On Fri, May 26, 2023 at 3:09=E2=80=AFAM Icenowy Zheng <uwu@icenowy.me>
> > wrote:
> > >=20
> > > 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.
> > >=20
> > > 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.
> > >=20
> > > 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.
> > >=20
> > > Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
> > > ---
> > > =C2=A0 arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi | 2 +-
> > > =C2=A0 1 file changed, 1 insertion(+), 1 deletion(-)
> >=20
> > 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.
> >=20
> > Reviewed-by: Douglas Anderson <dianders@chromium.org>
> >=20
> > ...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:
> >=20
> > Fixes: c2d94f72140a ("arm64: dts: mediatek: mt8173-elm: Move
> > display
> > to ps8640 auxiliary bus")
>=20
> 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)

>=20
> Anyway, for this commit:
>=20
> Reviewed-by: AngeloGioacchino Del Regno
> <angelogioacchino.delregno@collabora.com>