linux-kernel - Re: [PATCH] arm64: dts: qcom: sc7180: Switch pompom to the generic edp-panel

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Date:   Thu, 14 Dec 2023 12:58:04 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Bjorn Andersson <andersson@...nel.org>
Cc:     Stephen Boyd <swboyd@...omium.org>, Andy Gross <agross@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        cros-qcom-dts-watchers@...omium.org, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: qcom: sc7180: Switch pompom to the generic
 edp-panel



On 12/14/23 01:35, Douglas Anderson wrote:
> Pompom has several sources for its panel. Let's switch it to the
> generic edp-panel compatible string to account for this.
> 
> This fixes a problem where the panel wouldn't come up on some pompon
> devices after commit fb3f43d50d9b ("drm/panel-edp: Avoid adding
> multiple preferred modes"). Specifically, some models of pompom have a
> 1920x1080 panel which is _very_ different than the 1366x768 panel
> specified in the dts. Before the recent panel-edp fix on Linux things
> kinda/sorta worked because the panel-edp driver would include both the
> hardcoded and probed mode, AKA:
> 
> * #0 1920x1080
>    60.00 1920 1944 1960 2000 1080 1083 1088 1111 133320
>    flags: nhsync, nvsync; type: preferred, driver
> * #1 1366x768
>    60.00 1366 1406 1438 1500 768 773 778 900 81000
>    flags: nhsync, nvsync; type: preferred, driver
> 
> ...and, at least on ChromeOS, the userspace was consistently picking
> the first mode even though both were marked as "preferred". Now that
> the Linux driver is fixed we only get the hardcoded mode. That means
> we end up trying to drive a 1920x1080 panel at 1366x768 and it doesn't
> work so well.
> 
> Let's switch over to the generic panel-edp.
> 
> Fixes: fb3f43d50d9b ("drm/panel-edp: Avoid adding multiple preferred modes")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
Acked-by: Konrad Dybcio <konrad.dybcio@...aro.org>

Konrad