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

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Date:   Tue, 13 Dec 2022 16:34:56 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Doug Anderson <dianders@...omium.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



On 13.12.2022 16:23, Doug Anderson wrote:
> 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 prefer to keep it open-coded, it's just 8150 and 8250 that have
these simple fuse values, other SoCs have random numbers (check A618/
619 above, for example).. Plus the returned values might as well be
made-up, as it's just for opp matching.


> 
> 
> 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.
That's out of the scope of this patch, as it concerns all the
speedbin-supported GPUs. The returned value feeds 1<<ret, which
should be capped a bit lower than UINT_MAX, anyway. But I can
look into that in a separate patchset.

Konrad
> 
> -Doug