Re: [PATCH 09/12] Do more checks for proposed flip pixmaps

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Jul 30, 2014 at 11:01:48PM -0700, Keith Packard wrote:
> Eric Anholt <eric@anholt.net> writes:
> 
> > Keith Packard <keithp@keithp.com> writes:
> >
> >> Make sure the pitch and tiling are correct.
> >> Make sure there's a BO we can get at.
> >
> > I thought we couldn't change these parameters, but now I can't find what
> > prevents them from changing.  Can you cite sources?
> 
> Looks like we *can* change tiling format. That actually makes me kinda
> happy as that explains why we were able to allocate a linear frame
> buffer for the X front buffer (due to a bug) and page flip to DRI3
> buffers which are always tiled.
> 
> However, we can't change the pitch. From the kernel driver:
> 
> 	/*
> 	 * TILEOFF/LINOFF registers can't be changed via MI display flips.
> 	 * Note that pitch changes could also affect these register.
> 	 */
> 	if (INTEL_INFO(dev)->gen > 3 &&
> 	    (fb->offsets[0] != crtc->primary->fb->offsets[0] ||
> 	     fb->pitches[0] != crtc->primary->fb->pitches[0]))
> 		return -EINVAL;
> 
> I'll remove the tiling check.

Now that we have mmio flips in the kernel we can start to relax that
restriction. That still needs a bit more work in the mmio flip code
but I believe some people working on just that.

We could even change the pixel format, except a check was added to
drm_mode_page_flip_ioctl() to prevent that, so I guess it was
deemed that the API isn't meant to allow that.

-- 
Ville Syrjälä
Intel OTC