linux-kernel - Re: [PATCH 4/7] drm/msm/a6xx: Add support for A650 speed binning

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Date:   Tue, 13 Dec 2022 07:23:40 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, andersson@...nel.org,
        agross@...nel.org, krzysztof.kozlowski@...aro.org,
        marijn.suijten@...ainline.org, 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>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Chia-I Wu <olvaffe@...il.com>, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] drm/msm/a6xx: Add support for A650 speed binning

Hi,

On Mon, Dec 12, 2022 at 4:24 PM Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>
> Add support for matching QFPROM fuse values to get the correct speed bin
> on A650 (SM8250) GPUs.
>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 2c1630f0c04c..f139ec57c32d 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -1887,6 +1887,20 @@ static u32 a640_get_speed_bin(u32 fuse)
>         return UINT_MAX;
>  }
>
> +static u32 a650_get_speed_bin(u32 fuse)
> +{
> +       if (fuse == 0)
> +               return 0;
> +       else if (fuse == 1)
> +               return 1;
> +       else if (fuse == 2)
> +               return 2;
> +       else if (fuse == 3)
> +               return 3;
> +
> +       return UINT_MAX;

Unlike some of the other functions, you don't need any complexity. Just do:

if (fuse <= 3)
  return fuse;

return UINT_MAX;


I'd also suggest that perhaps "UINT_MAX" isn't exactly the right
return value for when we have an unrecognized fuse. The return type
for the function is "u32" which is a fixed size type. UINT_MAX,
however, is a type that is automatically sized by the compiler. Though
it's unlikely, theoretically a compiler could be configured such that
"unsigned int" was something other than 32 bits. Ideally either the
return type would be changed to "unsigned int" or you'd return
0xffffffff as the sentinel value.

-Doug