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

[Boris Brezillon]

On Wed, 2 Sep 2026 16:44:24 +0100
Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx> wrote:

> 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.

You're absolutely right, sorry for the brainfart.