[Nouveau] [PATCH 0/4] Allow ASYNC flip with atomic helpers.

[Daniel Vetter]

On Tue, Jan 17, 2017 at 12:14:24AM +0200, Laurent Pinchart wrote:
> Hi Harry,
> 
> On Monday 16 Jan 2017 16:13:39 Harry Wentland wrote:
> > On 2017-01-16 03:39 PM, Laurent Pinchart wrote:
> > > On Monday 16 Jan 2017 10:44:54 Andrey Grodzovsky wrote:
> > >> This series is a folow-up on
> > >> https://patchwork.kernel.org/patch/9501787/
> > >> 
> > >> The first patch makes changes to atomic helpers
> > >> to allow for drives with ASYNC flip support to use them.
> > >> Patches 2 and 3 are to use this in AMDGPU/DC and
> > >> patch 4 is possible cleanup in nouveau/kms who seems
> > >> to have the duplicate the helper as we did to support
> > >> ASYNC flips.
> > > 
> > > I have my doubts regarding this. I'd much rather see userspace moving to
> > > the atomic API instead of extending support for legacy APIs.
> > 
> > This change is not about introducing the async flag but cleaning up the
> > legacy helpers to make sure drivers that currently use it through the
> > legacy IOCTLs can benefit from the helpers and not have to roll their own.
> > 
> > If the problem is with the pflip_flags, wouldn't drivers still need that
> > after moving userspace to the atomic IOCTL?
> > 
> > I don't disagree with you on having userspace move to atomic but I don't
> > expect to see all userspace drivers move to atomic in the next couple
> > months. Why not clean this up in the meantime?
> 
> If this patch series was just about moving common driver code into the core, 
> sure, but it goes beyond that. Or, actually, it needs to go beyond that, but 
> doesn't yet. Removing the DRM_MODE_PAGE_FLIP_ASYNC test in patch 1/4 means 
> that the DRM core will not reject async page flips anymore, for any driver 
> that uses the helper. You thus need to either patch all drivers that use the 
> helper to reject the flag, or implement the feature in the drivers (and 
> preferably in the helpers then). The current version of this patch series will 
> make all existing users of the helpers accept async page flips without 
> actually implementing them.

"How do we check for this driver feature" was one of the opens I raised
here on irc, even before Andrey started typing :-) Definitely needs to be
addressed. What's imo optional is exposing async flips through the atomic
ioctl, since atm no atomic userspace seems to be in need of async flips
yet. And the semantics of multi-plane async flips are tricky to define
properly, so definitely want that userspace validation. That's why I think
just doing the compat stuff is ok.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch