Re: [PATCH v2 1/3] drm/msm/a5xx: Reset the GPU when resuming it

[Dmitry Baryshkov]

On Mon, Oct 19, 2026 at 11:05:08PM -0300, Fabricio Akio wrote:
> On SDM630, SDM660 and MSM8998 the GPU's GX power domain belongs to its
> SMMU, not to the GPU, so GX switches off only once the SMMU suspends as
> well. A GPU resumed with GX still on keeps its state, and the CP keeps
> its ringbuffer read pointer. a5xx_hw_init() then rewinds the ringbuffer
> and writes CP_ME_INIT at its start, while the CP goes on from its old
> position, executes stale ringbuffer contents and hangs:
> 
>   timeout waiting to drain ringbuffer 0 rptr/wptr = 23/C
> 
> Soft reset the GPU in a5xx_pm_resume() once it is powered, so that
> every resume starts from the reset state. The downstream driver resets
> only when it finds the GPU's power left on; resetting a GPU that was
> powered off changes nothing, and on A508 the reset takes about 2 us of
> a resume of about 1.5 ms, so do it every time.
> 
> The reset also clears the busy counter, which msm_gpu_pm_resume() has
> just sampled as devfreq's baseline. Take the baseline again after the
> reset, or the next devfreq poll subtracts the old count from the new
> one, wraps, and sets the GPU to its top frequency.
> 
> Signed-off-by: Fabricio Akio <fabricioakio@xxxxxxxxx>
> ---
> Changes in v2:
> - Take devfreq's busy-cycle baseline again after the reset, which
>   clears the busy counter (Sashiko)
> 
> Tested on A508 only; the reset runs on every A5xx.
> 
> A stall with the same signature, the CP's read pointer past the write
> pointer just after CP_ME_INIT, was reported on an A509:
> https://lore.kernel.org/linux-arm-msm/20260308-adreno-ringbuffer-drain-timeout-recovery-v1-1-985a33faf108@xxxxxxxxxxxxxxxx/
> This may be the root cause of the A509 stall Paul Sajna reported there.
> ---
>  drivers/gpu/drm/msm/adreno/a5xx_gpu.c | 15 +++++++++++++++
>  drivers/gpu/drm/msm/msm_gpu.h         |  1 +
>  drivers/gpu/drm/msm/msm_gpu_devfreq.c | 17 +++++++++++++++++
>  3 files changed, 33 insertions(+)
> 

Tested-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>


-- 
With best wishes
Dmitry