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
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>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
include/drm/drm_atomic.h | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index cf8e1220a4ac..09bef1b6c170 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -372,8 +372,22 @@ 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 never change this flag, it is only under the control
+ * of userspace.
*/
bool allow_modeset : 1;
/**
--
2.40.1
