Re: [PATCHv4 04/13] drm/shmobile: Restrict plane loops to only operate on legacy planes

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Apr 01, 2014 at 05:27:33PM +0200, Laurent Pinchart wrote:
> Hi Daniel,
> 
> On Friday 28 March 2014 18:53:40 Daniel Vetter wrote:
> > On Fri, Mar 28, 2014 at 06:52:50PM +0100, Daniel Vetter wrote:
> > > On Fri, Mar 28, 2014 at 04:50:13PM +0100, Laurent Pinchart wrote:
> > > > On Thursday 27 March 2014 17:44:29 Matt Roper wrote:
> > > > > Ensure that existing driver loops over all planes do not change
> > > > > behavior when we begin adding new types of planes (primary and cursor)
> > > > > to the DRM plane list in future patches.
> > > > > 
> > > > > Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> > > > > Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> > > > 
> > > > Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > > 
> > > > I have a question though. The patch set introduces three plane types,
> > > > OVERLAY, PRIMARY and CURSOR. What should a driver that has no concept
> > > > of primary plane do ? Expose all planes as OVERLAY planes only ?
> > > 
> > > It's a matter of backwards compat with old userspace. primary/cursor are
> > > simply ways to tell the drm core which planes to use to forward the legacy
> > > cursor crtc and which plane will be used for the framebuffer in setCrtc.
> > > 
> > > So until we have the new atomic interface ready your driver kinda needs to
> > > expose at least a primary plane, otherwise there's no way to even switch
> > > on the crtc.
> > > 
> > > But besides this backwards compat issue there's no difference and you can
> > > specify whatever plane you want as primary/cursor (or none if you don't
> > > care about old userspace).
> > 
> > Well the NULL primary plane probably needs a bit of work on top of Matt's
> > patch series here ...
> 
> It's the NULL primary plane I'm interested about, to allow a "root" plane not 
> to span the whole display. I have no urgent need for this though, I was just 
> curious to see if that feature was planned.

That should work and is kinda one of the features we want ot enable with
this. At least on i915 with a bit of frobbing we should be able to allow a
root/primary fb not spanning the entire crtc (with black as background
color). Or entirely disable the primary plane and just display a (again
boxed) yuv plane for fullscreen video with aspect ratio mismatching.

When I talk that NULL primary plane needs work I mean a driver which
doesn't register _any_ primary plane at all and only supports
free-floating over planes. So wouldn't work with fbcon or any current
generic userspace at all, but would allow you to reassign all planes to a
single crtc (if your hw can do it) without pulling tricks with fake
primary planes.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch