Re: [PATCH] drm/atomic: Filter out redundant DPMS calls

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Feb 20, 2025 at 10:53:57AM +0100, Simona Vetter wrote:
> On Wed, Feb 19, 2025 at 06:02:39PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Video players (eg. mpv) do periodic XResetScreenSaver() calls to
> > keep the screen on while the video playing. The modesetting ddx
> > plumbs these straight through into the kernel as DPMS setproperty
> > ioctls, without any filtering whatsoever. When implemented via
> > atomic these end up as full commits on the crtc, which leads to a
> > dropped frame every time XResetScreenSaver() is called.
> 
> I think you should add here that it's just an empty commit, because we do
> filter out redundant commits where crtc->active_changed does nothing.
> Except we still run the entire machinery with timestamps and drm_event and
> everything.
> 
> And I don't think it's worth to filter that out at the atomic level,
> because it's really only legacy ioctl that had this "complete noop"
> behaviour.
> 
> With the commit message augmented:
> 
> Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
> 
> Might also be nice to have a igt for this?

kms_flip was basically doing everything we want already,
so added one more subtest for this:
https://lore.kernel.org/igt-dev/20250228194240.20023-1-ville.syrjala@linux.intel.com/T/#u

> Plus also wondering whether we
> should cc: stable it.

I guess we could. I've been running this for who knows how long
anyway (just never got around to sending it), so should be fairly
safe.

-- 
Ville Syrjälä
Intel