linux-kernel - Re: [PATCH 1/4] ARM: dts: qcom: msm8974: add gpu support

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Date:   Sun, 24 Jan 2021 15:56:06 +0100
From:   Konrad Dybcio <konrad.dybcio@...ainline.org>
To:     Iskren Chernev <iskren.chernev@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Andy Gross <agross@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht,
        Samuel Pascua <pascua.samuel.14@...il.com>,
        Alexey Minnekhanov <alexeymin@...tmarketos.org>,
        Brian Masney <masneyb@...tation.org>
Subject: Re: [PATCH 1/4] ARM: dts: qcom: msm8974: add gpu support

Hi,

> +		gpu_opp_table: opp_table {
> +			status = "disabled";

Is there a good reason to disable this?

> +			opp-800000000 {
> +				opp-hz = /bits/ 64 <800000000>;
> +			};

No. A330 can't go lightspeed (unless there's some secret ultra-binned msm8974pro-v4-ad-5g). [1]

> +
> +			opp-500000000 {
> +				opp-hz = /bits/ 64 <500000000>;
> +			};
> +
> +			opp-275000000 {
> +				opp-hz = /bits/ 64 <275000000>;
> +			};
> +		};

IMHO we should create separate DTs for all revisions of 8974 (sigh) and keep the opp tables in there, only leaving a lowest-common-denominator one here (which according to downstream and the msm/drm driver would be 27000000 /27MHz/) to make it at least probe for everybody..

On a note, max GPU frequencies (based on [1] and grepping for gpu-pwrlevels or qcom,gpu-freq downstream) are:

* 578 MHz for PRO (so -AC)

* 550 MHz is mentioned in [1] but not downstream..

* 450 MHz for everything else (v2.2 has more DVFS steps)

> +			// iommus = <&gpu_iommu 0>;

I *think* you're going to need more gpu contexts (user/priv/spare), but don't quote me on that.

Konrad

[1] https://www.anandtech.com/show/7846/the-difference-between-snapdragon-800-and-801-clearing-up-confusion