linux-kernel - Re: [PATCH 09/17] drm/msm/a6xx: Switch to GMU AO counter

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Message-ID: <0a2188e7-3919-48f7-b5c1-8f779f617f28@oss.qualcomm.com>
Date: Wed, 23 Jul 2025 12:19:11 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Akhil P Oommen <akhilpo@....qualcomm.com>,
        Rob Clark <robin.clark@....qualcomm.com>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/17] drm/msm/a6xx: Switch to GMU AO counter

On 7/20/25 2:16 PM, Akhil P Oommen wrote:
> CP_ALWAYS_ON counter falls under GX domain which is collapsed during
> IFPC. So switch to GMU_ALWAYS_ON counter for any CPU reads since it is
> not impacted by IFPC. Both counters are clocked by same xo clock source.
> 
> Signed-off-by: Akhil P Oommen <akhilpo@....qualcomm.com>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 30 ++++++++++++++++--------------
>  1 file changed, 16 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 6770f0363e7284e4596b1188637a4615d2c0779b..f000915a4c2698a85b45bd3c92e590f14999d10d 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -16,6 +16,19 @@
>  
>  #define GPU_PAS_ID 13
>  
> +static u64 read_gmu_ao_counter(struct a6xx_gpu *a6xx_gpu)
> +{
> +	u64 count_hi, count_lo, temp;
> +
> +	do {
> +		count_hi = gmu_read(&a6xx_gpu->gmu, REG_A6XX_GMU_ALWAYS_ON_COUNTER_H);
> +		count_lo = gmu_read(&a6xx_gpu->gmu, REG_A6XX_GMU_ALWAYS_ON_COUNTER_L);
> +		temp = gmu_read(&a6xx_gpu->gmu, REG_A6XX_GMU_ALWAYS_ON_COUNTER_H);
> +	} while (count_hi != temp);

The original logic is as follows:

static u64 gen7_read_alwayson(struct adreno_device *adreno_dev)
{
        struct kgsl_device *device = KGSL_DEVICE(adreno_dev);
        u32 lo = 0, hi = 0, tmp = 0;

        /* Always use the GMU AO counter when doing a AHB read */
        gmu_core_regread(device, GEN7_GMU_ALWAYS_ON_COUNTER_H, &hi);
        gmu_core_regread(device, GEN7_GMU_ALWAYS_ON_COUNTER_L, &lo);

        /* Check for overflow */
        gmu_core_regread(device, GEN7_GMU_ALWAYS_ON_COUNTER_H, &tmp);

        if (hi != tmp) {
                gmu_core_regread(device, GEN7_GMU_ALWAYS_ON_COUNTER_L,
                                &lo);
                hi = tmp;
        }

        return (((u64) hi) << 32) | lo;
}

Doing this in a while-loop almost looks like you want a lot of time to
pass - REG_WIDTH(u32?)/19.2 MHz

Konrad