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

[Chris Wilson]

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? We have CRC support on pnv right?
-Chris