[Intel-gfx] [PATCH 2/5] drm/i915: Always prepare planes at the start of an atomic commit

[Chris Wilson]

On Tue, Nov 15, 2016 at 10:37:09AM +0100, Daniel Vetter wrote:
> On Tue, Nov 15, 2016 at 08:58:14AM +0000, Chris Wilson wrote:
> > The generic atomic helper likes to skip a prepare_plane_fb() if it
> > decides that the plane->fb is unchanged. This is wrong for us for a
> > couple of reasons:
> > 
> >  - if the pipe is reconfigured (i.e. a size change) but the framebuffer
> >    is untouched, we still have to flush any rendering prior to the
> >    reconfiguration to prevent wait-for-scanline GPU hangs
> > 
> >  - if the framebuffer is rotated, it remains the same but has a
> >    different view and a different address.
> > 
> > Finally, even if the framebuffer is unchanged the flip/modeset should be
> > ordered with respect to rendering to the frontbuffer.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> 
> This is directly against
> 
> commit fcc60b413d14dd06ddbd79ec50e83c4fb2a097ba
> Author: Keith Packard <keithp at keithp.com>
> Date:   Sat Jun 4 01:16:22 2016 -0700
> 
>     drm: Don't prepare or cleanup unchanging frame buffers [v3]
> 
> and I'm pretty sure that was tested on i915.

That patch is bogus. But if we want plane granularity, the helpers are
not sufficient either.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre