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From: Daniel Vetter <daniel.vetter <at> ffwll.ch>
Subject: [PATCH 00/17] atomic modeset core<->driver interfaces and helpers
Newsgroups: gmane.comp.video.dri.devel
Date: Sunday 2nd November 2014 13:19:13 UTC (over 4 years ago)
Hi all,

So here's my atomic series, finally debugged. This is just the
core<->driver interface plus a big pile of helpers. Short recap of the main

- There are essentially three helper libraries in this patch set:

  * Transitional helpers to use the new plane callbacks for legacy plane
    updates and in the crtc helper's ->mode_set callback. These helpers are
    only temporarily used to convert drivers to atomic, but they allow a
    nice separation between changing the driver backend and switching to
    the atomic commit logic.

  * Legacy helpers to implement all the legacy driver entry points
    (page_flip, set_config, plane vfuncs) on top of the new atomic driver
    interface. These are completely driver agnostic. The reason for having
    the legacy support as helpers is that drivers can switch step-by-step.
    And they could e.g. even keep the legacy page_flip code around for some
    old platforms where converting to full-blown atomic isn't worth it.

  * Atomic helpers which implement the various new ->atomic_* driver
    interfaces in terms of the revised crtc helper and new plane helper

- The revised crtc helper implemenation essentially implements all the
  lessons learned in the i915 modeset rework (when using the atomic helpers

  * Enable/disable sequence for a given config are always the same and
    callbacks are always called in the same order. This contrast starkly
    with the crtc helpers, where the sequence of operations is heavily
    dependent on the previous config.

    One corollary of this is that if the configuration of a crtc only
    partially changes (e.g. a connector moves in a cloned config) the
    helper code will still disable/enable the full display pipeline. This
    is the only way to ensure that the enable/disable sequence is always
    the same.

  * It won't call disable or enable hooks more than once any more because
    it lost track of state, thanks to the atomic state tracking. And if
    drivers implement the ->reset hook properly (by either resetting the hw
    or reading out the hw state into the atomic structures) this even
    extends to the hardware state. So no more disable-me-harder kind of

  * The only lacking thing is the hw state readout/cross-check support, but
    if drivers have hw state readout support in their ->reset handlers it's
    simple to extend that to cross-check the hw state.

  * The crtc->mode_set callback is gone and its replacement only sets crtc
    timings an no longer updates the primary plane state. This way we can
    finally implement primary planes properly.

- The new plane helpers should be suitable enough for pretty much
  everything, and a perfect fit for hardware with GO bits. Even if they
  don't fit the atomic helper library is rather flexible and exports all
  the functions for the individual steps to drivers. So drivers can pick
  what matches and implement their own magic for everything.

- A big difference compared to all previous atomic series is that this one
  doesn't implement async commit in a generic way. Imo driver requirements
  for that are too diverse to create anything reasonable sane which would
  actually work on a reasonable amount of different drivers. Also, we've
  never had a helper library for page_flips even, so it's really hard to
  know what might work and what's stupid without a bit of experience.

  I think with the current flexibility for drivers to pick individual
  stages and existing helpers like drm_flip_queue it's rather easy though
  to implement proper async commit.

- There's a few other differences of minor importance to earlier atomic

  * Common/generic properties are parsed in the callers/core and not in
    drivers, and passed to drivers by directly setting the right members in
    atomic state structures. That greatly simplifies all the transitional
    and legacy helpers an removes a lot of boilerplate code.

  * There's no crazy trylock mode used for the async commit since these
    helpers don't do async commit. A simple ordered flip queue of atomic
    state updates should be sufficient for preventing concurrent hw access
    anyway, as long as synchronous updates stall correctly with e.g.
    flush_work_queue or similar function.

  * These helpers reuse the existing ->mode_fixup hooks in the atomic_check
    callback. Which means that drivers need to adapat and move a lot less
    into their atomic_check callbacks.

Now this isn't everything needed in the drm core and helpers for full
atomic support. But it's enough to start with converting drivers, and
except for actually testing multiplane and multicrtc updates also enough to
implement full atomic updates. Still missing are:

- Per-plane locking. Since these helpers here encapsulate the locking
  completely this should be fairly easy to implement.

- fbdev support for atomic_check/commit, so that multi-pipe finally works

- Adding and decoding shared/core properties. That just needs to be rebased
  from Rob's latest patch series, with minor adjustments so that the
  decoding happens in the core instead of in drivers.

- Actually adding the atomic ioctl. Again just rebasing Rob's latest patch
  should be all that's needed.

- Finally I couldn't test connector/encoder stealing properly since my test
  vehicle here doesn't allow a connector on different crtcs. So drivers
  which support this might see some surprises in that area.

As just mentioned I've done a fake conversion of an existing driver using
crtc helpers to debug the helper code and validate the smooth transition
approach. And that smooth transition was the really big motivation for
this. It seems to actually work and consists of 3 phases:

Phase 1: Rework driver backend for crtc/plane helpers

The requirement here is that universal plane support is already implement.
When that's done there's two big things to do:

- Split up the existing ->update/disable_plane hooks into check/commit
  hooks and extract the crtc-wide prep/flush parts (like setting/clearing
  GO bits).

- The other big change is to split the crtc->mode_set hook into the plane
  update (done using the plane helpers) and the crtc setup in a new
  ->mode_set_nofb hook.

When phase 1 is complete the driver implements all the new callbacks which
push the software state into hardware, but still using all the legacy entry
points and crtc helpers. The transitional helpers serve as impendance
mismatch here.

Phase 2: Rework state handling

This consists of rolling out the state handling helpers for planes, crtcs
and connectors and reviewing all ->mode_fixup and similar hooks to make
sure they don't depend upon implicit global state which might change. Any
such code must be moved into ->atomic_check functions which just rely on
the free-standing atomic state update structures.

This phase also adds a few small pieces of fixup code to make sure the
atomic state doesn't get out of sync in the legacy driver callbacks.

Phase 3: Roll out atomic support

Now it's just about replacing vfuncs with the ones provided by the helper
and filling out the small missing pieces (like atomic_check logic or async
commit support needed for page_flips). Due to the prep work in phase 1 no
changes to the driver backend functions should be required, and because of
the prep work in phase 2 atomic implementations can be rolled out
step-by-step. So if async commit ins't implemented yet page_flip can be
implemented with the legacy functions without wreaking havoc in the other

I'm working on a blog post to go a bit more into details of the conversion,

The entire pile of patches is available at


That branch includes the somewhat stubbed-out and hackish conversion of
but it should be good enough to demonstrate the ideas and concepts.

Since I've wasted so much time getting exynos going here and so many people
eagerly waiting for this I want to send the pull request to Dave in the
next few
days if possible. So please bring on all the review, comments and feedback

Cheers, Daniel

Daniel Vetter (17):
  drm: Move drm_crtc_init from drm_crtc.h to drm_plane_helper.h
  drm: Pull drm_crtc.h into the kerneldoc template
  drm: fixup kerneldoc in drm_crtc.h
  drm/modeset_lock: document trylock_only in kerneldoc
  drm: Add atomic driver interface definitions for objects
  drm: Global atomic state handling
  drm: Add atomic/plane helpers
  drm/plane-helper: transitional atomic plane helpers
  drm/crtc-helper: Transitional functions using atomic plane helpers
  drm: Atomic crtc/connector updates using crtc/plane helper interfaces
  drm/atomic-helper: implementatations for legacy interfaces
  drm/atomic: Integrate fence support
  drm/atomic-helpers: document how to implement async commit
  drm/atomic-helper: implement ->page_flip
  drm/atomic-helpers: functions for state duplicate/destroy/reset
  drm: Docbook integration and over sections for all the new helpers
  drm/atomic: Refcounting for plane_state->fb

 Documentation/DocBook/drm.tmpl             |   28 +-
 drivers/gpu/drm/Makefile                   |    4 +-
 drivers/gpu/drm/armada/armada_crtc.c       |    1 +
 drivers/gpu/drm/ast/ast_mode.c             |    1 +
 drivers/gpu/drm/bochs/bochs_kms.c          |    1 +
 drivers/gpu/drm/cirrus/cirrus_mode.c       |    1 +
 drivers/gpu/drm/drm_atomic.c               |  615 +++++++++
 drivers/gpu/drm/drm_atomic_helper.c        | 1906
 drivers/gpu/drm/drm_crtc_helper.c          |  132 ++
 drivers/gpu/drm/drm_plane_helper.c         |  198 ++-
 drivers/gpu/drm/gma500/psb_intel_display.c |    1 +
 drivers/gpu/drm/mgag200/mgag200_mode.c     |    1 +
 drivers/gpu/drm/nouveau/dispnv04/crtc.c    |    1 +
 drivers/gpu/drm/nouveau/nv50_display.c     |    1 +
 drivers/gpu/drm/omapdrm/omap_crtc.c        |    1 +
 drivers/gpu/drm/qxl/qxl_display.c          |    1 +
 drivers/gpu/drm/radeon/radeon_display.c    |    1 +
 drivers/gpu/drm/rcar-du/rcar_du_crtc.c     |    1 +
 drivers/gpu/drm/shmobile/shmob_drm_crtc.c  |    1 +
 drivers/gpu/drm/sti/sti_drm_crtc.c         |    1 +
 drivers/gpu/drm/tegra/dc.c                 |    1 +
 drivers/gpu/drm/tilcdc/tilcdc_crtc.c       |    1 +
 drivers/gpu/drm/udl/udl_modeset.c          |    1 +
 drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c        |    1 +
 drivers/gpu/drm/vmwgfx/vmwgfx_scrn.c       |    1 +
 drivers/staging/imx-drm/imx-drm-core.c     |    1 +
 include/drm/drm_atomic.h                   |   65 +
 include/drm/drm_atomic_helper.h            |   97 ++
 include/drm/drm_crtc.h                     |  245 +++-
 include/drm/drm_crtc_helper.h              |   13 +
 include/drm/drm_modeset_lock.h             |    1 +
 include/drm/drm_plane_helper.h             |   38 +
 32 files changed, 3326 insertions(+), 36 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_atomic.c
 create mode 100644 drivers/gpu/drm/drm_atomic_helper.c
 create mode 100644 include/drm/drm_atomic.h
 create mode 100644 include/drm/drm_atomic_helper.h


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