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Message-ID: <d23b9b5defeb9399436df0674a04dfd2f90aad73.camel@icenowy.me>
Subject: Re: [PATCH] arm64: dts: mediatek: mt8173-elm: remove panel model
 number in DT
From:   Icenowy Zheng <uwu@icenowy.me>
To:     Matthias Brugger <matthias.bgg@gmail.com>,
        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>,
        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:   Tue, 30 May 2023 13:03:39 +0800
In-Reply-To: <3069dcf7-28e0-e7f6-11d5-9bc286d7d6e3@gmail.com>
References: <20230526100801.16310-1-uwu@icenowy.me>
         <CAD=FV=UxrFVZXn+dtgamttTVopWMSVbxYsHCGG_tS+3OTXbHiw@mail.gmail.com>
         <f4a9e090-3712-200e-bd09-70090c9cccbc@collabora.com>
         <6996788b112f4795d2930a6664b3152cd9a380a8.camel@icenowy.me>
         <3069dcf7-28e0-e7f6-11d5-9bc286d7d6e3@gmail.com>
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=E5=9C=A8 2023-05-29=E6=98=9F=E6=9C=9F=E4=B8=80=E7=9A=84 18:28 +0200=EF=BC=
=8CMatthias Brugger=E5=86=99=E9=81=93=EF=BC=9A
>=20
>=20
> On 29/05/2023 10:45, Icenowy Zheng wrote:
> > =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=C2=A0 arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi | 2 +-
> > > > > =C2=A0=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.
> >=20
> > Well at least I developed this patch on v6.3.
> >=20
> > (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
>=20
> I applied the patch without the fixes tag. Lets stay on the secure
> side to not=20
> break older kernels.

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

Should we cc stable@vger.kernel.org ?

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