drm/atomic-helper: nonblocking commit support

Design ideas:

- split up the actual commit into different phases, and have
  completions for each of them. This will be useful for the future
  when we want to interleave phases much more aggressively, for e.g.
  queue depth > 1. For not it's just a minimal optimization compared
  to current common nonblocking implementation patterns from drivers,
  which all stall for the entire commit to complete, including vblank
  waits and cleanups.

- Extract a separate atomic_commit_hw hook since that's the part most
  drivers will need to overwrite, hopefully allowing even more shared
  code.

- Enforce EBUSY seamntics by attaching one of the completions to the
  flip_done vblank event. Side benefit of forcing atomic drivers using
  these helpers to implement event handlign at least semi-correct. I'm
  evil that way ;-)

- Ridiculously modular, as usual.

- The main tracking unit for a commit stays struct drm_atomic_state,
  and the ownership rules for that are unchanged. Ownership still
  gets transferred to the driver (and subsequently to the worker) on
  successful commits. What is added is a small, per-crtc, refcounted
  structure to track pending commits called struct drm_crtc_commit.
  No actual state is attached to that though, it's purely for ordering
  and waiting.

- Dependencies are implicitly handled by assuming that any CRTC part
  of &drm_atomic_state is a dependency, and that the current commit
  must wait for any commits to complete on those CRTC. This way
  drivers can easily add more depencies using
  drm_atomic_get_crtc_state(), which is very natural since in most
  case a dependency exists iff there's some bit of state that needs to
  be cross checked.

  Removing depencies is not possible, drivers simply need to be
  careful to not include every CRTC in a commit if that's not
  necessary. Which is a good idea anyway, since that also avoids
  ww_mutex lock contention.

- Queue depth > 1 sees some prep work in this patch by adding a stall
  paramater to drm_atomic_helper_swap_states(). To be able to push
  commits entirely free-standing and in a deeper queue through the
  back-end the driver must not access any obj->state pointers. This
  means we need to track the old state in drm_atomic_state (much
  easier with the consolidated arrays), and pass them all explicitly
  to driver backends (this will be serious amounts of churn).

  Once that's done stall can be set to false in swap_states.

v2: Dont ask for flip_done signalling when the CRTC is off and stays
off: Drivers don't handle events in that case. Instead complete right
away. This way future commits don't need to have special-case logic,
but can keep blocking for the flip_done completion.

v3: Tons of fixes:
- Stall for preceeding commit for real, not the current one by
  accident.
- Add WARN_ON in case drivers don't fire the drm event.
- Don't double-free drm events.

v4: Make legacy cursor not stall.

v5: Extend the helper hook to cover the entire commit tail. Some
drivers need special code for cleanup and vblank waiting, this makes
it a bit more useful. Inspired by the rockchip driver.

v6: Add WARN_ON to catch drivers who forget to send out the
drm event.

v7: Fixup the stalls in swap_state for real!!

v8:
- Fixup trailing whitespace, spotted by Maarten.
- Actually wait for flip_done in cleanup_done, like the comment says
  we should do. Thanks a lot for Tomeu for helping with debugging this
  on.

v9: Now with awesome kerneldoc!

v10: Split out drm_crtc_commit tracking infrastructure.

v:
- Add missing static (Gustavo).
- Split out the sync functions, only do the actual nonblocking
  logic in this patch (Maarten).

Cc: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Tested-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Tomeu Vizoso <tomeu.vizoso@gmail.com>
Cc: Daniel Stone <daniels@collabora.com>
Tested-by: Liviu Dudau <Liviu.Dudau@arm.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Testcase: igt/kms_flip/*
Testcase: igt/kms_cursor*
Testcase: igt/kms*plane*
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465388359-8070-10-git-send-email-daniel.vetter@ffwll.ch

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