[PATCH xserver] xf86-video-modesetting: Fix ms_queue_vblank(flags = MS_QUEUE_RELATIVE)

[Alex Goins]

Change 677c32bc refactored all usages of drmWaitVBlank() into a helper function,
ms_queue_vblank().

ms_queue_vblank() takes in an MS_QUEUE_RELATIVE flag to indicate that the
sequence number is relative rather than absolute, but still treats the actual
sequence number as absolute, passing it through ms_crtc_msc_to_kernel_msc()
unconditionally before calling drmWaitVBlank().

ms_crtc_msc_to_kernel_msc() works by subtracting a vblank offset from the
provided sequence number, which only makes sense for absolute sequence numbers.
In the case of PRIME Sync, drmmode_SharedPixmapPrsentOnVBlank() passes in 1,
which results in a large negative vblank offset. After subtracting, we're left
with a relative sequence number of 100,000+, i.e. wait for 100,000+ vblanks...

In the relative case we want to pass in the sequence number unmodified. Simply
add a check to do this.

Signed-off-by: Alex Goins <agoins at nvidia.com>
---
 hw/xfree86/drivers/modesetting/vblank.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/xfree86/drivers/modesetting/vblank.c b/hw/xfree86/drivers/modesetting/vblank.c
index 31cf0bd..fe046e4 100644
--- a/hw/xfree86/drivers/modesetting/vblank.c
+++ b/hw/xfree86/drivers/modesetting/vblank.c
@@ -219,7 +219,8 @@ ms_queue_vblank(xf86CrtcPtr crtc, ms_queue_flag flags,
         if (flags & MS_QUEUE_NEXT_ON_MISS)
             vbl.request.type |= DRM_VBLANK_NEXTONMISS;
 
-        vbl.request.sequence = ms_crtc_msc_to_kernel_msc(crtc, msc);
+        vbl.request.sequence = (flags & MS_QUEUE_RELATIVE) ?
+                                    msc : ms_crtc_msc_to_kernel_msc(crtc, msc);
         vbl.request.signal = seq;
         ret = drmWaitVBlank(ms->fd, &vbl);
         if (ret == 0) {
-- 
2.7.4