linux-kernel - Re: [PATCH 2/3] arm64: dts: qcom: msm8939: Add missing MDSS reset

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Message-ID: <d10424b3-b70f-4166-adca-f81fcb214e04@oss.qualcomm.com>
Date: Mon, 15 Sep 2025 15:42:45 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Stephan Gerhold <stephan.gerhold@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: Vincent Knecht <vincent.knecht@...loo.org>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Rob Herring
 <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] arm64: dts: qcom: msm8939: Add missing MDSS reset

On 9/15/25 3:28 PM, Stephan Gerhold wrote:
> On most MSM8939 devices, the bootloader already initializes the display to
> show the boot splash screen. In this situation, MDSS is already configured
> and left running when starting Linux. To avoid side effects from the
> bootloader configuration, the MDSS reset can be specified in the device
> tree to start again with a clean hardware state.
> 
> The reset for MDSS is currently missing in msm8939.dtsi, which causes
> errors when the MDSS driver tries to re-initialize the registers:
> 
>  dsi_err_worker: status=6
>  dsi_err_worker: status=6
>  dsi_err_worker: status=6
>  ...
> 
> It turns out that we have always indirectly worked around this by building
> the MDSS driver as a module. Before v6.17, the power domain was temporarily
> turned off until the module was loaded, long enough to clear the register
> contents. In v6.17, power domains are not turned off during boot until
> sync_state() happens, so this is no longer working. Even before v6.17 this
> resulted in broken behavior, but notably only when the MDSS driver was
> built-in instead of a module.
> 
> Cc: stable@...r.kernel.org
> Fixes: 61550c6c156c ("arm64: dts: qcom: Add msm8939 SoC")
> Signed-off-by: Stephan Gerhold <stephan.gerhold@...aro.org>
> ---

Reviewed-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>

Konrad