[PATCH 14/17] drm/msm: add atomic support

[Rob Clark]

On Tue, May 27, 2014 at 6:09 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Tue, May 27, 2014 at 04:06:28PM -0400, Rob Clark wrote:
>> On Tue, May 27, 2014 at 3:26 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
>
> [snip]
>
>> Well, there was the NONBLOCK atomic flag.. I'm not entirely sure if we
>> should hang so much off of that one flag.
>
> Yeah, a separate VBLANK_SYNCED might be useful. Apparently people also
> want non-blocking modesets.
>
> [snip]
>
>> > I think one excellent use-case we get for free (almost) without the ioctl
>> > would be fbcon. It very much wants to do an atomic update, so converting
>> > that over to the atomic interface would be good imo.
>>
>> Yes, iirc the remaining non-atomic paths are fbcon related.  In
>> principle it should be a simple matter to increment the refcnt on
>> fbcon state object and re-apply it.  Although at the moment we keep
>> track of *how* to apply the state (ie. page_flip vs set_config, etc)
>> as the state object is built up.. which isn't very conducive to
>> re-committing an existing state object.  Which is part of the reason I
>> wanted to deprecate the various existing
>> ->page_flip/->update_plane/->set_config/etc and introduce per object
>> ->commit()'s.  (Which could either be called by helpers, or called
>> internally by driver or completely ignored by driver)
>
> Yeah, I think the approach in here with a few helpers to bend atomic
> ->commit to the old hooks (somewhat-ish) is good. And with the crtc
> helpers we should be able to move most drivers away from the old hooks
> quickly. The exception will be pageflips/cursors, but that requires a lot
> of driver-specific work, and probably first a full conversion to universal
> planes (which atm don't support everything even for the primary plane due
> to the arbitrary restriction to rgbx8888).

btw, I guess/hope most SoC drivers (ie. the ones that want to do crazy
things with overlays) would be moving rapidly away from using primary
plane helpers.  I think native primary planes fits better most of the
non-trivial mobile display controller blocks..

>> I've been a bit reluctant so far to do too much additional refactoring
>> on top of atomic, since I'm about at the limit of what I have time to
>> repeatedly rebase each kernel version.  This is why I'm a bit anxious
>> to start merging some of atomic, even if it doesn't do absolutely
>> everything yet.
>
> I understand that, which is why I suggested a bunch of things to split out
> already so we can get them in.
>
> On top of that I think with the split-up mode_config.mutex like I've just
> proposed in an RFC we have a clear path for the locking issues, too. So
> could go ahead an merge the w/w conversion, too.

I suppose now that I split modeset acquire ctx out into it's own thing
(originally it was inline w/ drm_atomic_state), I could reshuffle the
patches and move ww_mutex stuff below atomic.. will take a bit of
patch surgery since some parts of that patch would have to move to
later patches, but I can sort it out

> That leaves the set_prop refactoring which is still under discussion.
> Those three pieces hopefully help a lot with reducing rebasing pain.
>
> On top of that I think we should look at cutting away functional pieces of
> the conversion, e.g. ignore planes at first and only look at atomic
> modeset. Or ignore atomic modesets and only look at plane updates,
> rejecting anything that changes connectors or crtcs. By cutting out slices
> we should be able to get patches into shape step-by-step.

hmm, well, not sure how much value it is splitting up like that.  I
suppose the only-plane approach would sidestep/punt some issues.  But
once locking and set_prop are in place / agreed, it isn't that much
more from a churn perspective.

tbh, I think the worse problems are when we actually expose atomic
ioctl to userspace.  Right now we are rather restricted in the updates
triggered via atomic in that there are fixed well defined entry points
to atomic.  Ie. only pageflip() sets _NONBLOCK flag, and it does not
set mode property, so you won't ever see a _NONBLOCK modeset.

BR,
-R

> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch