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

From: Alex Deucher
Date: Thu Oct 13 2016 - 10:55:28 EST


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>

> 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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