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.
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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