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Message-ID: <3069dcf7-28e0-e7f6-11d5-9bc286d7d6e3@gmail.com>
Date:   Mon, 29 May 2023 18:28:21 +0200
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Subject: Re: [PATCH] arm64: dts: mediatek: mt8173-elm: remove panel model
 number in DT
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To:     Icenowy Zheng <uwu@icenowy.me>,
        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
References: <20230526100801.16310-1-uwu@icenowy.me>
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 <f4a9e090-3712-200e-bd09-70090c9cccbc@collabora.com>
 <6996788b112f4795d2930a6664b3152cd9a380a8.camel@icenowy.me>
From:   Matthias Brugger <matthias.bgg@gmail.com>
In-Reply-To: <6996788b112f4795d2930a6664b3152cd9a380a8.camel@icenowy.me>
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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@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 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@collabora.com>
>