[Bug 91562] [SKL][Linux] : Xrandr is not working as expected

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91562

--- Comment #18 from Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com> ---
(In reply to Chris Wilson from comment #17)
> (In reply to Tvrtko Ursulin from comment #16)
> > (In reply to Chris Wilson from comment #15)
> > > (In reply to Tvrtko Ursulin from comment #14)
> > > > Created attachment 118122 [details]
> > > > ddx debug log in Y tiling mode
> > > > 
> > > > With the DDX rebuilt to default to Y tiling, this logs shows that when
> > > > "xrandr -o left" it abandons the Y tiled FB and goes back to X tiled.
> > > 
> > > It sets the rotation, and then the kernel rejects the setcrtc and so it is
> > > forced to use a shadowfb, X without rotation, and perform manual rotations
> > > (using the GPU of course!) from the Y-tiled frontbuffer to the X-tiled
> > > framebuffer.
> > 
> > Does it try to go Y tiled when attempting to rotate, in the default build? 
> 
> It's tricky. The buffer cannot be exported and Y-tiling is so much slower
> for common operations that I am not convinced it is worth it. It is possible
> for the client to provide a Y-tiled buffer that we will then use. But since
> the setcrtc failed...

So basically the reported black screen has nothing to do with hardware
rotation, since hardware rotation is not supported since it requires Y tiling
which the DDX won't attempt.

And either way, since I could not reproduce the black screen, someone else will
have to provide full debug logs for that case.

> > Interestingly in the Y tiled build there seems to be a path where it doesn't
> > use fb modifiers ("[drm:intel_framebuffer_init] No Y tiling for legacy
> > addfb").
> 
> Right, during the start up it tests whether the interface is deliberately
> broken.

I am pretty sure I've seen it when requesting rotation, not on startup.

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