linux-kernel - Re: [PATCH 1/7] drm/msm/a6xx: Fix unknown speedbin case

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Message-ID: <bjcjeixkmvhjv7nke65maknrckxjyosqsqpdf5i5v4iingfwj4@bkdhb2nbwbqg>
Date:   Tue, 17 Oct 2023 01:22:27 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
CC:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        <cros-qcom-dts-watchers@...omium.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>,
        Stephen Boyd <swboyd@...omium.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        Luca Weiss <luca.weiss@...rphone.com>,
        "Rob Clark" <robdclark@...omium.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 1/7] drm/msm/a6xx: Fix unknown speedbin case

On Tue, Sep 26, 2023 at 08:24:36PM +0200, Konrad Dybcio wrote:
> 
> When opp-supported-hw is present under an OPP node, but no form of
> opp_set_supported_hw() has been called, that OPP is ignored by the API
> and marked as unsupported.
> 
> Before Commit c928a05e4415 ("drm/msm/adreno: Move speedbin mapping to
> device table"), an unknown speedbin would result in marking all OPPs
> as available, but it's better to avoid potentially overclocking the
> silicon - the GMU will simply refuse to power up the chip.
> 
> Currently, the Adreno speedbin code does just that (AND returns an
> invalid error, (int)UINT_MAX). Fix that by defaulting to speedbin 0
> (which is conveniently always bound to fuseval == 0).

Wish we documented somewhere that we should reserve BIT(0) for fuse
val=0 always and assume that would be the super SKU.

Reviewed-by: Akhil P Oommen <quic_akhilpo@...cinc.com>

-Akhil

> 
> Fixes: c928a05e4415 ("drm/msm/adreno: Move speedbin mapping to device table")
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index d4e85e24002f..522ca7fe6762 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -2237,7 +2237,7 @@ static int a6xx_set_supported_hw(struct device *dev, const struct adreno_info *i
>  		DRM_DEV_ERROR(dev,
>  			"missing support for speed-bin: %u. Some OPPs may not be supported by hardware\n",
>  			speedbin);
> -		return UINT_MAX;
> +		supp_hw = BIT(0); /* Default */
>  	}
>  
>  	ret = devm_pm_opp_set_supported_hw(dev, &supp_hw, 1);
> 
> -- 
> 2.42.0
>