Re: [PATCH] Add virtio gpu driver.

On Tue, 31 May 2016 08:29:20 +0200
Gerd Hoffmann [off-list ref] wrote:

  Hi,

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Why attach the hotspot to the plane?  Wouldn't it make more sense to
make it a framebuffer property?  

We don't have properties on the framebuffer. I guess you /could/ just add
it internally to struct drm_framebuffer, and not bother exposing to
userspace. I guess that would be a lot simpler,  

Yes.  I can simply stick the hotspot into drm_framebuffer in
drm_mode_cursor_universal() and pick up the values in the driver's plane
update function.

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 but it also means that
atomic userspace can't use hotspots before we add properties to fbs. And
doing that is a bit tricky since drm_framebuffer objects are meant to be
invariant - this assumption is deeply in-grained into the code all over
the place, everything just compares pointers when semantically it means to
compare the entire fb (including backing storage pointer/offsets and
everything).  

Hmm, the hotspot location for a given cursor image is invariant too, so
I don't think that would be a big issue.

I'd expect userspace define a bunch of cursors, then switch between them
(instead of defining a single cursor, then constantly updating it).

Except updating a single cursor (well, two alternating buffers) is
exactly what Weston does, since there is no "set of cursors". On
Wayland, a cursor is just a regular surface like any other with
arbitrary content from a client, except it happens to be associated
with a pointer device.

Furthermore, in Weston a cursor plane is not special in any way. *Any*
client surface can go on the cursor plane if it fits. Universal planes,
and all that.

That's one existing userspace. I suppose that is sub-optimal for
virtual drivers, isn't it? But what else could Weston do without having
separate paths for "normal DRM" vs. "virtual DRM"?


Thanks,
pq