[PATCH 00/17] atomic modeset core<->driver interfaces and helpers

Daniel Vetter
2014-11-02T13:19:13Z

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
ideas:

- 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
hooks.

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

* 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
nonsense.

* 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
series:

* 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 code
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
sanely.

- 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
operations.

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

The entire pile of patches is available at

http://cgit.freedesktop.org/~danvet/drm/log/?h=colder-fusion

That branch includes the somewhat stubbed-out and hackish conversion of exynos,
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 are
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
quickly.

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

--
2.1.1

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org