On Sun, Dec 22, 2024 at 06:47:18AM +0200, Dmitry Baryshkov wrote:
> Hello,
>
> On Wed, 11 Oct 2023 at 12:20, Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:
> >
> > msm is automagically upgrading normal commits to full modesets, and
> > that's a big no-no:
> >
> > - for one this results in full on->off->on transitions on all these
> > crtc, at least if you're using the usual helpers. Which seems to be
> > the case, and is breaking uapi
> >
> > - further even if the ctm change itself would not result in flicker,
> > this can hide modesets for other reasons. Which again breaks the
> > uapi
> >
> > v2: I forgot the case of adding unrelated crtc state. Add that case
> > and link to the existing kerneldoc explainers. This has come up in an
> > irc discussion with Manasi and Ville about intel's bigjoiner mode.
> > Also cc everyone involved in the msm irc discussion, more people
> > joined after I sent out v1.
>
> I have been looking at the drm_atomic_helper_check_modeset() issue, I
> couldn't help but notice that this hasn't been committed.
> Maybe it's time for v3?
Oops. Working on it now.
-Sima
>
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> > Cc: Maxime Ripard <mripard@xxxxxxxxxx>
> > Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > Cc: David Airlie <airlied@xxxxxxxxx>
> > Cc: Daniel Vetter <daniel@xxxxxxxx>
> > Cc: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>
> > Cc: Rob Clark <robdclark@xxxxxxxxx>
> > Cc: Simon Ser <contact@xxxxxxxxxxx>
> > Cc: Manasi Navare <navaremanasi@xxxxxxxxxx>
> > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > Cc: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> > Cc: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > ---
> > include/drm/drm_atomic.h | 23 +++++++++++++++++++++--
> > 1 file changed, 21 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> > index cf8e1220a4ac..545c48545402 100644
> > --- a/include/drm/drm_atomic.h
> > +++ b/include/drm/drm_atomic.h
> > @@ -372,8 +372,27 @@ struct drm_atomic_state {
> > *
> > * Allow full modeset. This is used by the ATOMIC IOCTL handler to
> > * implement the DRM_MODE_ATOMIC_ALLOW_MODESET flag. Drivers should
> > - * never consult this flag, instead looking at the output of
> > - * drm_atomic_crtc_needs_modeset().
> > + * not consult this flag, instead looking at the output of
> > + * drm_atomic_crtc_needs_modeset(). The detailed rules are:
> > + *
> > + * - Drivers must not consult @allow_modeset in the atomic commit path,
> > + * and instead use drm_atomic_crtc_needs_modeset().
> > + *
> > + * - Drivers may consult @allow_modeset in the atomic check path, if
> > + * they have the choice between an optimal hardware configuration
> > + * which requires a modeset, and a less optimal configuration which
> > + * can be committed without a modeset. An example would be suboptimal
> > + * scanout FIFO allocation resulting in increased idle power
> > + * consumption. This allows userspace to avoid flickering and delays
> > + * for the normal composition loop at reasonable cost.
> > + *
> > + * - Drivers must consult @allow_modeset before adding unrelated struct
> > + * drm_crtc_state to this commit by calling
> > + * drm_atomic_get_crtc_state(). See also the warning in the
> > + * documentation for that function.
> > + *
> > + * - Drivers must never change this flag, it is only under the control
> > + * of userspace.
> > */
> > bool allow_modeset : 1;
> > /**
> > --
> > 2.40.1
> >
>
>
> --
> With best wishes
> Dmitry
--
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
