Re: [PATCH] drm/msm/adreno: keep the GPU timestamp monotonic across power collapse

[Dmitry Baryshkov]

On Tue, Sep 08, 2026 at 09:03:55AM +0200, Konrad Dybcio wrote:
> On 8/28/26 1:13 AM, Dmitry Baryshkov wrote:
> > The always-on counter behind MSM_PARAM_TIMESTAMP sits in the GPU power
> > domain on a4xx, a5xx and the GMU-less a6xx parts, so it restarts from
> > zero whenever the GPU is powered up again and the timestamp reported to
> > userspace jumps backwards. On an a702 six reads three seconds apart all
> > land in the 500..1200 tick range, stepping backwards twice, and on an
> > a530 the OpenCL device timer conformance test fails because
> > clGetDeviceAndHostTimer() returns an end time below the start time.
> > 
> > Save the counter in the suspend path of the affected generations, while
> > the GPU is still powered, and add the accumulated ticks to the value
> > reported to userspace.
> > 
> > Assisted-by: LLM
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
> > ---
> > The always-on counter behind MSM_PARAM_TIMESTAMP sits in the GPU power
> > domain on a4xx, a5xx and the GMU-less a6xx parts, so it restarts from zero
> > whenever the GPU is powered up again and the timestamp userspace reads
> > jumps backwards.  Accumulate what the counter reached before each suspend
> > and add it to what is reported afterwards.
> 
> Could (some) a5xx parts use A5XX_GPMU_ALWAYS_ON_COUNTER/0xa879?
> msm-3.x defines it as KGSL_PERFCOUNTER_NOT_USED fwiw..

It seems it also restarts on power collapse (so always on is not
actually always). Also if it worked, it would have helped only a530 and
a540 (MSM8996 and MSM8998), leaving SDM630/660 and all MSM8956/76/53/37
without the fix.

-- 
With best wishes
Dmitry