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

[Matthias Brugger]

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@xxxxxxxxxx>
> > > 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@xxxxxxxxxx>
> > > > ---
> > > >    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@xxxxxxxxxxxx>
> > >
> > > ...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.

Regards,
Matthias

> > Anyway, for this commit:
> >
> > Reviewed-by: AngeloGioacchino Del Regno
> > <angelogioacchino.delregno@xxxxxxxxxxxxx>