Re: [PATCH v7 14/17] drm/panfrost: Avoid cache flush after perfcnt sample in fully coherent systems

[Adrián Larumbe]

On 01.09.2026 15:37, Boris Brezillon wrote:
> On Fri, 28 Aug 2026 21:56:54 +0100
> Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx> wrote:
> 
> > If the GPU and CPU are fully coherent, then there's no need to flush the
> > GPU caches after a perfcnt sample is made available.
> > 
> > Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/panfrost/panfrost_perfcnt.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_perfcnt.c b/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> > index ffc77121070e..b3f71d7fd82a 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> > @@ -52,7 +52,10 @@ void panfrost_perfcnt_clean_cache_done(struct panfrost_device *pfdev)
> >  
> >  void panfrost_perfcnt_sample_done(struct panfrost_device *pfdev)
> >  {
> > -	gpu_write(pfdev, GPU_CMD, GPU_CMD_CLEAN_CACHES);
> > +	if (pfdev->features.selected_coherency != COHERENCY_ACE)
> 
> I think ACE_LITE would allow us to skip the flush to, so

I thought ACE_LITE means the GPU can snoop CPU caches but not the other way round, so at the end of a
sample, we still have to flush GPU caches for the CPU to see counter data.

> 	if (pfdev->features.selected_coherency == COHERENCY_NONE)
> 
> > +		gpu_write(pfdev, GPU_CMD, GPU_CMD_CLEAN_CACHES);
> > +	else
> > +		complete(&pfdev->perfcnt->dump_comp);
> >  }
> >  
> >  static int panfrost_perfcnt_dump_locked(struct panfrost_device *pfdev)
> > 

Adrian Larumbe