[PATCH] drm: atomic: Clarify documentation around drm_atomic_crtc_needs_modeset

[Alex Deucher]

On Thu, Oct 13, 2016 at 5:47 AM, Brian Starkey <brian.starkey at arm.com> 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 at ffwll.ch>
> Signed-off-by: Brian Starkey <brian.starkey at arm.com>
> ---
>
> 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 at amd.com>

> 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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