Re: [PATCH] drm: atomic: Clarify documentation around drm_atomic_crtc_needs_modeset

[Daniel Vetter]

On Thu, Oct 13, 2016 at 10:54:51AM -0400, Alex Deucher wrote:
> On Thu, Oct 13, 2016 at 5:47 AM, Brian Starkey <brian.starkey@xxxxxxx> wrote:
> > Add some additional comments to more explicitly describe the meaning and
> > usage of the three CRTC modeset detection booleans: mode_changed,
> > connectors_changed and active_changed.
> >
> > Suggested-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > Signed-off-by: Brian Starkey <brian.starkey@xxxxxxx>
> > ---
> >
> > Hi Daniel,
> >
> > I guess I asked for this one :-), please just check my understanding
> > is correct.
> >
> 
> The whole thread was very enlightening for me with respect to those
> flags as well.  The patch looks good to me.
> Acked-by: Alex Deucher <alexander.deucher@xxxxxxx>

Applied to drm-misc, thanks.
-Daniel

> 
> > Thanks,
> > Brian
> >
> >  drivers/gpu/drm/drm_atomic_helper.c |    9 +++++----
> >  include/drm/drm_atomic.h            |   11 ++++++++++-
> >  include/drm/drm_crtc.h              |    5 +++++
> >  3 files changed, 20 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 78ea735..fb4071a 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -458,10 +458,11 @@ mode_fixup(struct drm_atomic_state *state)
> >   * removed from the crtc.
> >   * crtc_state->active_changed is set when crtc_state->active changes,
> >   * which is used for dpms.
> > + * See also: drm_atomic_crtc_needs_modeset()
> >   *
> >   * IMPORTANT:
> >   *
> > - * Drivers which update ->mode_changed (e.g. in their ->atomic_check hooks if a
> > + * Drivers which set ->mode_changed (e.g. in their ->atomic_check hooks if a
> >   * plane update can't be done without a full modeset) _must_ call this function
> >   * afterwards after that change. It is permitted to call this function multiple
> >   * times for the same update, e.g. when the ->atomic_check functions depend upon
> > @@ -510,9 +511,9 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
> >
> >         for_each_connector_in_state(state, connector, connector_state, i) {
> >                 /*
> > -                * This only sets crtc->mode_changed for routing changes,
> > -                * drivers must set crtc->mode_changed themselves when connector
> > -                * properties need to be updated.
> > +                * This only sets crtc->connectors_changed for routing changes,
> > +                * drivers must set crtc->connectors_changed themselves when
> > +                * connector properties need to be updated.
> >                  */
> >                 ret = update_connector_routing(state, connector,
> >                                                connector_state);
> > diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> > index d9aff06..1ce255f 100644
> > --- a/include/drm/drm_atomic.h
> > +++ b/include/drm/drm_atomic.h
> > @@ -368,8 +368,17 @@ int __must_check drm_atomic_nonblocking_commit(struct drm_atomic_state *state);
> >   *
> >   * To give drivers flexibility struct &drm_crtc_state has 3 booleans to track
> >   * whether the state CRTC changed enough to need a full modeset cycle:
> > - * connectors_changed, mode_changed and active_change. This helper simply
> > + * connectors_changed, mode_changed and active_changed. This helper simply
> >   * combines these three to compute the overall need for a modeset for @state.
> > + *
> > + * The atomic helper code sets these booleans, but drivers can and should
> > + * change them appropriately to accurately represent whether a modeset is
> > + * really needed. In general, drivers should avoid full modesets whenever
> > + * possible.
> > + *
> > + * For example if the CRTC mode has changed, and the hardware is able to enact
> > + * the requested mode change without going through a full modeset, the driver
> > + * should clear mode_changed during its ->atomic_check.
> >   */
> >  static inline bool
> >  drm_atomic_crtc_needs_modeset(struct drm_crtc_state *state)
> > diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> > index c4a3164..1f094d2 100644
> > --- a/include/drm/drm_crtc.h
> > +++ b/include/drm/drm_crtc.h
> > @@ -116,6 +116,11 @@ struct drm_plane_helper_funcs;
> >   * never return in a failure from the ->atomic_check callback. Userspace assumes
> >   * that a DPMS On will always succeed. In other words: @enable controls resource
> >   * assignment, @active controls the actual hardware state.
> > + *
> > + * The three booleans active_changed, connectors_changed and mode_changed are
> > + * intended to indicate whether a full modeset is needed, rather than strictly
> > + * describing what has changed in a commit.
> > + * See also: drm_atomic_crtc_needs_modeset()
> >   */
> >  struct drm_crtc_state {
> >         struct drm_crtc *crtc;
> > --
> > 1.7.9.5
> >
> > _______________________________________________
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> > dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch