diff options
| -rw-r--r-- | include/drm/drm_atomic.h | 23 |
1 files changed, 21 insertions, 2 deletions
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h index 4d7f4c5f2001..02c2ffd95a3e 100644 --- a/include/drm/drm_atomic.h +++ b/include/drm/drm_atomic.h @@ -376,8 +376,27 @@ 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(). + * 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 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 only under the control + * of userspace. */ bool allow_modeset : 1; /** |