[Intel-gfx] [PATCH 09/12] Do more checks for proposed flip pixmaps

Ville Syrjälä ville.syrjala at linux.intel.com
Thu Jul 31 07:43:18 PDT 2014

On Wed, Jul 30, 2014 at 11:01:48PM -0700, Keith Packard wrote:
> Eric Anholt <eric at anholt.net> writes:
> > Keith Packard <keithp at 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

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