The introduction of primary planes has apparently caused a bit of fb
refcounting fun for people. That makes it a good time to clean up the
arcane rules and slight differences between ->update_plane and
->set_config. The new rules are:

- The core holds a reference for both the new and the old fb (if
  they're non-NULL of course) while calling into the driver through
  either ->update_plane or ->set_config.

- Drivers may not clobber plane->fb if their callback fails. If they
  do that, they need to store a pointer to the old fb in it again.
  When calling into the driver plane->fb still points at the current
  (old) framebuffer.

- The core will update the plane->fb pointer on success. Drivers can
  do that themselves too, but aren't required to any more for the
  primary plane.

- The core will update fb refcounts for the plane->fb pointer,
  presuming the drivers hold up their end of the bargain.

v2: Remove now unused tmpfb (Thierry)

v3: Drop broken changes from drm_mode_setplane (Ville). Also polish
the commit message a bit.

v4: Also fix up the handling of ->disable_plane in
drm_plane_force_disable. The issue was that we didn't save plane->fb
over the ->disable_plane call. Just paranoia, nothing relies on this.

v5: Keep still useful comments about directly calling ->set_config,
which I should have done for v4 already. Requested by Matt.

Cc: Thierry Reding <treding@nvidia.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: NMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

By the time drm_mode_config_cleanup calls this all the hw state should
be cleaned up already - we even have a WARN right before calling
plane->destroy callbacks asserting that all framebuffers are gone.

So trying to disable things harder is a bit a bug. Caught by Thierry
since it resulted in some mode_config.mutex locking backtraces.

Cc: Thierry Reding <treding@nvidia.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: NThierry Reding <treding@nvidia.com>
Tested-by: NThierry Reding <treding@nvidia.com>
Reviewed-by: NMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

The src_w / src_h parameters to update_plane include a subpixel offset;
we need to shift off the subpixel bits before comparing to CRTC size
when checking for primary plane scaling.
Signed-off-by: NMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

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: NDaniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

Add a new drm_crtc_init_with_planes() to allow drivers to provide
specific primary and cursor planes at CRTC initialization.  The existing
drm_crtc_init() interface remains to avoid driver churn in existing
drivers; it will initialize the CRTC with a plane helper-created primary
plane and no cursor plane.

v2:
  - Move drm_crtc_init() to plane helper file so that nothing in the DRM
    core depends on helpers.  [suggested by Daniel Vetter]
  - Keep cursor parameter to drm_crtc_init_with_planes() a void* until
    we actually add cursor support.  [suggested by Daniel Vetter]
Signed-off-by: NMatt Roper <matthew.d.roper@intel.com>
Reviewed-by: NRob Clark <robdclark@gmail.com>

When we expose non-overlay planes to userspace, they will become
accessible via standard userspace plane API's.  We should be able to
handle the standard plane operations against primary planes in a generic
way via the modeset handler.

Drivers that can program primary planes more efficiently, that want to
use their own primary plane structure to track additional information,
or that don't have the limitations assumed by the helpers are free to
provide their own implementation of some or all of these handlers.

v3: Tweak kerneldoc formatting slightly to avoid ugliness
v2:
 - Move plane helpers to a new file (drm_plane_helper.c)
 - Tighten checks on update handler (check for scaling, CRTC coverage,
   subpixel positioning)
 - Pass proper panning parameters to modeset interface
 - Disallow disabling primary plane (and thus CRTC) if other planes are
   still active on the CRTC.
 - Use a minimal format list that should work on all hardware/drivers.
   Drivers may call this function with a more accurate plane list to
   enable additional formats they can support.
Signed-off-by: NMatt Roper <matthew.d.roper@intel.com>
Reviewed-by: NRob Clark <robdclark@gmail.com>