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authorDaniel Vetter <daniel.vetter@ffwll.ch>2014-04-15 04:02:43 -0400
committerDave Airlie <airlied@redhat.com>2014-04-17 23:18:50 -0400
commitb6ccd7b9873dc46becd11838c885d5c783784156 (patch)
tree1b9336f6be71f908854d77b2ca975943bea58e2c /Documentation/DocBook
parenta82049b1f1aeb02818092455cd43134ef83d81ea (diff)
drm/plane-helper: Don't fake-implement primary plane disabling
After thinking about this topic a bit more I've reached the conclusion that implementing this doesn't make sense: - The locking is all wrong: set_config(NULL) will also unlink encoders and connectors, but those links are protected with the mode_config mutex. In the ->disable_plane callback we only hold all modeset locks, but eventually we want to switch to just grabbing the per-crtc (and maybe per-plane) locks as needed, maybe based on ww_mutexes. Having a callback which absolutely needs all modeset locks is bad for this conversion. Note that the same isn't true for the provided ->update_plane since we've audited the crtc helpers to make sure that not encoder or connector links are changed. - There's no way to re-enable the plane with an ->update_plane: The connectors/encoder links are lost and so we can't re-enable the CRTC. Even without that issue the driver might have reassigned some shared resources (as opposed to e.g. DPMS off, where drivers are not allowed to do that to make sure the CRTC can be enabled again). - The semantics don't make much sense: Userspace asked to scan out black (or some other color if the driver supports a background color), not that the screen be disabled. - Implementing proper primary plane support (i.e. actually disabling the primary plane without disabling the CRTC) is really simple, at least if all the hw needs is flipping a bit. The big task is auditing all the interactions with other ioctls when the CRTC is on but there's no primary plane (e.g. pageflips). And some of that work still needs to be done. Cc: Matt Roper <matthew.d.roper@intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Matt Roper <matthew.d.roper@intel.com> Signed-off-by: Dave Airlie <airlied@redhat.com>
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