Re: [PATCH 2/2] drm/msm/a6xx: Use CX AO Counter register for timestamp on a750 GPUs

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 9/8/26 3:24 PM, Neil Armstrong wrote:
> The a750 uses the CX AO Counters instead of the GMU_ALWAYS_ON_COUNTER
> register on A6xx and other A7xx GPUs, use it when running a A750 GPU.
> 
> Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index f9de9329dee3..081e79ea4652 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -23,9 +23,15 @@ static u64 a6xx_gmu_get_timestamp(struct msm_gpu *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);
> +		if (adreno_is_a750_family(adreno_gpu)) {
> +			count_hi = gmu_read(&a6xx_gpu->gmu, REG_A7XX_GMU_CX_AO_COUNTER_H);
> +			count_lo = gmu_read(&a6xx_gpu->gmu, REG_A7XX_GMU_CX_AO_COUNTER_L);
> +			temp = gmu_read(&a6xx_gpu->gmu, REG_A7XX_GMU_CX_AO_COUNTER_H);

KGSL apparently *writes* the system time to these registers, is that
an idiosyncrasy regarding how the vendor userland drivers then use
this counter?

Konrad

P.S. looks like a8xx also has this counter