linux-kernel - Re: [PATCH] arm64: dts: qcom: sm8550-qrd: add display and panel

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Message-ID: <894282af-fdfa-d476-fe9a-677db6483501@linaro.org>
Date:   Tue, 16 May 2023 17:36:06 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Neil Armstrong <neil.armstrong@...aro.org>,
        "Signed-off-by : Abel Vesa" <abel.vesa@...aro.org>
Subject: Re: [PATCH] arm64: dts: qcom: sm8550-qrd: add display and panel



On 16.05.2023 17:35, Krzysztof Kozlowski wrote:
> On 16/05/2023 17:26, Konrad Dybcio wrote:
>>>>> +&mdss_mdp {
>>>>> +	status = "okay";
>>>>> +};
>>>> This should also be enabled by default, MDSS is useless when MDP is
>>>> disabled.
>>>
>>> But don't we want to disable both when display is not used (not connected)?
>> The MDSS bus device only has a 0x1000 slice of the 0x90000-long "full MDSS",
>> the rest is probed with MDP/DPU. It also calls of_something_populate that
>> make DSI, DSIPHY and DP/HDMI probe. But all of them ultimately need a graph
>> handle to MDP.
>>
>> If we have a display (of any kind), MDP has to be enabled (or the display
>> engine will not have a way to be programmed).
>>
>> If we don't, enabling MDSS makes no sense as all of the hardware will be
>> shut down right after probing.
>>
>> So I'd say either both or none.
> 
> Yes, so the current state - both disabled - is matching it.
Right, but what i was trying to say is that if we leave MDP without
any status properties, it will follow MDSS.

Konrad
> 
> Best regards,
> Krzysztof
>