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

[Neil Armstrong]

On 9/9/26 11:06, Konrad Dybcio wrote:
> 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@xxxxxxxxxx>
> > ---
> >   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?

This is a GMU counter, no sure why & how KGSL or freedreno would write anything to it...

> Konrad
>
> P.S. looks like a8xx also has this counter