[PATCH v2 weston 00/16] Atomic modesetting support

[Daniel Vetter]

On Tue, Jun 23, 2015 at 12:48 PM, Daniel Stone <daniel at fooishbar.org> wrote:
>> This is assuming we cannot do without the primary plane. If it was
>> possible to drive truely universal planes, we would not know if we need
>> a primary plane until we know if there is anything on it. You'd have to
>> first assume the primary plane is needed, test the additional plane
>> setups, and then if we don't need the primary plane, test once more
>> without it.
>
> Sure, in theory the primary plane can be disabled, but that's not the
> reality of a lot of common hardware, so we'll have to deal with that
> assumption for a very long time to come.

Just a quick clarification discussed with Daniel on irc: Restrictions
on requiring an enabled primary plane are mostly just software since
the default primary plane enabled by universal planes can't do
anything else. It can also only do rgbx8888.

But atomic (and already even the transitional plane helpers) lift that
restriction, and drivers must take explicit action in their
atomic_check callbacks to refuse a config with enabled crtc but
disabled primary. The default assumption is that primary/cursor planes
aren't anything special at all compared to other planes and only used
for implementing backwards compatibility with old userspace.

The only thing where this differes is that for cursors and primary
planes we have dedicated properties to tell userspace the size limits,
for sprites there's nothing like that. But givin that max size is just
a small part of figuring out what kind of surfaces a driver supports I
don't think that's a big deal really ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch