linux-kernel - Re: [PATCH 3/9] arm64: dts: qcom: sc7280: Enable MDP turbo mode

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Date: Thu, 22 Feb 2024 10:32:06 -0800
From: Abhinav Kumar <quic_abhinavk@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>
CC: Bjorn Andersson <quic_bjorande@...cinc.com>,
        Douglas Anderson
	<dianders@...omium.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul
	<sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        "David
 Airlie" <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        <cros-qcom-dts-watchers@...omium.org>,
        Bjorn Andersson
	<andersson@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <freedreno@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH 3/9] arm64: dts: qcom: sc7280: Enable MDP turbo mode



On 2/22/2024 1:46 AM, Dmitry Baryshkov wrote:
> On Thu, 22 Feb 2024 at 11:28, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>>
>>
>>
>> On 2/22/24 10:04, Dmitry Baryshkov wrote:
>>> On Thu, 22 Feb 2024 at 10:56, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>>>>
>>>>
>>>>
>>>> On 2/22/24 00:41, Dmitry Baryshkov wrote:
>>>>> On Thu, 22 Feb 2024 at 01:19, Bjorn Andersson <quic_bjorande@...cinc.com> wrote:
>>>>>>
>>>>>> The max frequency listed in the DPU opp-table is 506MHz, this is not
>>>>>> sufficient to drive a 4k@60 display, resulting in constant underrun.
>>>>>>
>>>>>> Add the missing MDP_CLK turbo frequency of 608MHz to the opp-table to
>>>>>> fix this.
>>>>>
>>>>> I think we might want to keep this disabled for ChromeOS devices. Doug?
>>>>
>>>> ChromeOS devices don't get a special SoC
>>>
>>> But they have the sc7280-chrome-common.dtsi, which might contain a
>>> corresponding /delete-node/ .
>>
>> What does that change? The clock rates are bound to the
>> SoC and the effective values are limited by link-frequencies
>> or the panel driver.
> 
> Preventing the DPU from overheating? Or spending too much power?
> 

Running DPU clock in turbo is a requirement to support 4k@60 otherwise 
the pixel rate that high cannot be supported.

sc7280 chrome devices already limit to HBR2

https://lore.kernel.org/all/20230329233416.27152-1-quic_abhinavk@quicinc.com/

So the DPU will not vote more than nominal.

And like others wrote, limiting SOC frequencies is not the way and we 
should filter out required frequencies using link-frequencies.

Hence fwiw, I am fine with this change.


Reviewed-by: Abhinav Kumar <quic_abhinavk@...cinc.com>