From: Simona Vetter simona.vetter@ffwll.ch
[ Upstream commit c5e3306a424b52e38ad2c28c7f3399fcd03e383d ]
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
v2: I forgot the case of adding unrelated crtc state. Add that case and link to the existing kerneldoc explainers. This has come up in an irc discussion with Manasi and Ville about intel's bigjoiner mode. Also cc everyone involved in the msm irc discussion, more people joined after I sent out v1.
v3: Wording polish from Pekka and Thomas
Acked-by: Pekka Paalanen pekka.paalanen@collabora.com Acked-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@gmail.com Cc: Daniel Vetter daniel@ffwll.ch Cc: Pekka Paalanen pekka.paalanen@collabora.com Cc: Rob Clark robdclark@gmail.com Cc: Simon Ser contact@emersion.fr Cc: Manasi Navare navaremanasi@google.com Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: Abhinav Kumar quic_abhinavk@quicinc.com Cc: Dmitry Baryshkov dmitry.baryshkov@linaro.org Signed-off-by: Simona Vetter simona.vetter@intel.com Signed-off-by: Simona Vetter simona.vetter@ffwll.ch Link: https://patchwork.freedesktop.org/patch/msgid/20250108172417.160831-1-simona... Signed-off-by: Sasha Levin sashal@kernel.org --- include/drm/drm_atomic.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h index 10b1990bc1f68..36225aedf6138 100644 --- a/include/drm/drm_atomic.h +++ b/include/drm/drm_atomic.h @@ -372,8 +372,27 @@ 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(). + * generally not consult this flag, but instead look at the output of + * drm_atomic_crtc_needs_modeset(). The detailed rules are: + * + * - Drivers must not consult @allow_modeset in the atomic commit path. + * Use drm_atomic_crtc_needs_modeset() instead. + * + * - Drivers must consult @allow_modeset before adding unrelated struct + * drm_crtc_state to this commit by calling + * drm_atomic_get_crtc_state(). See also the warning in the + * documentation for that function. + * + * - Drivers must never change this flag, it is under the exclusive + * control of userspace. + * + * - 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. */ bool allow_modeset : 1; /**