[Intel-gfx] [PATCH] drm/i915: Fix cursor updates on some platforms

[Ville Syrjälä]

On Fri, Jul 14, 2017 at 05:24:03PM +0100, Chris Wilson wrote:
> Quoting ville.syrjala at linux.intel.com (2017-07-14 16:52:27)
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > Turns out that just writing CURPOS isn't sufficient to move the cursor
> > on some platforms. My 830 works just fine, but eg. 945 and PNV don't.
> > On those platforms we need to arm even the CURPOS update with a
> > CURBASE write.
> > 
> > Even worse, a write to any of the cursor register apart from CURBASE
> > will cancel an already pending cursor update. So if we have armed a
> > CURCNTR/CURBASE update, a subsequent CURPOS write prior to vblank
> > would cancel that armed update. Thus we're left with a cursor that
> > doesn't appear to move, or even change shape.
> > 
> > Fix the problem by always performing the CURBASE write after a
> > CURPOS write. Bspec is somewhat unclear which platforms actually
> > require this CURBASE write and which don't. So to keep it simple
> > and to make sure we really fix the problem across all supported
> > devices, let's just perform the CURBASE write unconditionally.
> 
> Hmm, it seems that kms_cursor_crc should catch this? I guess we are
> missing a move N times quickly test?

Yeah. I guess what we have is basically this:
1. enable cursor at some location
2. wait for vblank and grab the crc
3. disable cursor and render the cursor image to the primary plane fb
4. wait for vblank and grab the crc

I guess what we could do is make step 1 enable the cursor at an
incorrect location, and then perform a few extra cursor movements,
ending in the correct location, before we grab the crc.

> We have CRC support on pnv right?

We should have it across the board.

-- 
Ville Syrjälä
Intel OTC