linux-kernel - Re: [Freedreno] [PATCH 5/6] drm/msm/a6xx: Use GMU_ALWAYS_ON_COUNTER for GMU-equipped GPUs in timestamp

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Date:   Wed, 17 May 2023 14:09:26 -0400
From:   Jonathan Marek <jonathan@...ek.ca>
To:     Konrad Dybcio <konrad.dybcio@...aro.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>
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        freedreno@...ts.freedesktop.org
Subject: Re: [Freedreno] [PATCH 5/6] drm/msm/a6xx: Use GMU_ALWAYS_ON_COUNTER
 for GMU-equipped GPUs in timestamp

AFAIK GMU_ALWAYS_ON_COUNTER does not have the same value as 
CP_ALWAYS_ON_COUNTER (only the same frequency), so changing this would 
break userspace expecting to be able to compare the value returned by 
MSM_PARAM_TIMESTAMP with CP timestamp values.

On 5/17/23 12:50 PM, Konrad Dybcio wrote:
> Use the always-on counter provided by the GMU to skip having to
> keep the GPU online.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
>   drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 9 +++------
>   1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 8707e8b6ac7e..d2a999b90589 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -1664,12 +1664,9 @@ static int a6xx_get_timestamp(struct msm_gpu *gpu, uint64_t *value)
>   
>   	mutex_lock(&a6xx_gpu->gmu.lock);
>   
> -	/* Force the GPU power on so we can read this register */
> -	a6xx_gmu_set_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
> -
> -	*value = gpu_read64(gpu, REG_A6XX_CP_ALWAYS_ON_COUNTER);
> -
> -	a6xx_gmu_clear_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
> +	*value = gmu_read64(&a6xx_gpu->gmu,
> +			    REG_A6XX_GMU_ALWAYS_ON_COUNTER_L,
> +			    REG_A6XX_GMU_ALWAYS_ON_COUNTER_H);
>   
>   	mutex_unlock(&a6xx_gpu->gmu.lock);
>   
>