[PATCH] drm/radeon: Fix negative cursor position

[Takashi Iwai]

On Mon, 26 Sep 2016 10:57:50 +0200,
Michel D4nzer wrote:
> 
> On 23/09/16 10:06 PM, Takashi Iwai wrote:
> > radeon_cursor_move_unlock() contains a workaround for AVIVO chips that
> > are older than DCE6 when the cursor ends on 128 pixel boundary.  It
> > decreases the position when the calculated end position is on 128
> > pixel boundary.  However, it hits also the condition where x=-1 and
> > width=1 are passed, since cursor_end is 0 (which is aligned with 128,
> > too).  Then the value gets decreased and it hits WARN_ON_ONCE()
> > below, eventually screws up the GPU.
> > 
> > The fix is simply to skip the workaround when x is already zero.
> > Also, remove the superfluous WARN_ON_ON() for the negative value check
> > that wouldn't happen any longer after this change.
> > 
> > Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1000433
> > Cc: <stable at vger.kernel.org>
> > Signed-off-by: Takashi Iwai <tiwai at suse.de>
> > ---
> >  drivers/gpu/drm/radeon/radeon_cursor.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/radeon/radeon_cursor.c b/drivers/gpu/drm/radeon/radeon_cursor.c
> > index 2a10e24b34b1..4e436eb49a56 100644
> > --- a/drivers/gpu/drm/radeon/radeon_cursor.c
> > +++ b/drivers/gpu/drm/radeon/radeon_cursor.c
> > @@ -193,10 +193,8 @@ static int radeon_cursor_move_locked(struct drm_crtc *crtc, int x, int y)
> >  			if (w <= 0) {
> >  				w = 1;
> >  				cursor_end = x - xorigin + w;
> > -				if (!(cursor_end & 0x7f)) {
> > +				if (x > 0 && !(cursor_end & 0x7f))
> >  					x--;
> > -					WARN_ON_ONCE(x < 0);
> > -				}
> >  			}
> 
> The problem with this change is that the horizontal cursor end position
> can again and up as a multiple of 128, which this code is trying to
> avoid, because it can break the cursor with some versions of AVIVO / DCE
> display engines.
> 
> Attached is a proof-of-concept (only compile tested) alternative fix
> which hides the cursor while it's out of bounds. I'll test it, clean it
> up and split it up into multiple patches when I get a chance, but maybe
> you or the reporter of the referenced bug can test it in the meantime.

Sure, I'll ask the reporter to test with your tentative fix.
Thanks!


Takashi