[Mesa-dev] [PATCH 5/5] glx: Handle out-of-sequence swap completion events correctly.

[Mario Kleiner]

The code for emitting INTEL_swap_events swap completion
events needs to translate from 32-Bit sbc on the wire to
64-Bit sbc for the events and handle wraparound accordingly.

It assumed that events would be sent by the server in the
order their corresponding swap requests were emitted from
the client, iow. sbc count should be always increasing. This
was correct for DRI2.

This is not always the case under the DRI3/Present backend,
where the Present extension can execute swaps and send out
completion events in a different order than the submission
order of the present requests. This confused the wraparound
handling. This patch fixes the problem by handling 32-Bit
wraparound in both directions. As long as successive swap
completion events real 64-Bit sbc's don't differ by more
than 2^30, this should be able to do the right thing.

Cc: "10.3 10.4" <mesa-stable at lists.freedesktop.org>
Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
---
 src/glx/glxext.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/glx/glxext.c b/src/glx/glxext.c
index 68c359e..fdc24d4 100644
--- a/src/glx/glxext.c
+++ b/src/glx/glxext.c
@@ -143,8 +143,13 @@ __glXWireToEvent(Display *dpy, XEvent *event, xEvent *wire)
       aevent->ust = ((CARD64)awire->ust_hi << 32) | awire->ust_lo;
       aevent->msc = ((CARD64)awire->msc_hi << 32) | awire->msc_lo;
 
-      if (awire->sbc < glxDraw->lastEventSbc)
-	 glxDraw->eventSbcWrap += 0x100000000;
+      /* Handle 32-Bit wire sbc wraparound in both directions to cope with out
+       * of sequence 64-Bit sbc's
+       */
+      if ((int64_t) awire->sbc < ((int64_t) glxDraw->lastEventSbc - 0x40000000))
+         glxDraw->eventSbcWrap += 0x100000000;
+      if ((int64_t) awire->sbc > ((int64_t) glxDraw->lastEventSbc + 0x40000000))
+         glxDraw->eventSbcWrap -= 0x100000000;
       glxDraw->lastEventSbc = awire->sbc;
       aevent->sbc = awire->sbc + glxDraw->eventSbcWrap;
       return True;
-- 
1.9.1