[Mesa-dev] [PATCH] dri3: Stricter SBC wraparound handling

[Michel Dänzer]

From: Michel Dänzer <michel.daenzer at amd.com>

Prevents spuriously bumping the upper 32 bits of the SBC, which results
in hangs with the modesetting driver from xserver 1.20.

Bugzilla: https://bugs.freedesktop.org/106351
Tested-by: Mike Lothian <mike at fireburn.co.uk>
Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>
---
 src/loader/loader_dri3_helper.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/loader/loader_dri3_helper.c b/src/loader/loader_dri3_helper.c
index 6db8303d26d..f0ff2f07bde 100644
--- a/src/loader/loader_dri3_helper.c
+++ b/src/loader/loader_dri3_helper.c
@@ -370,9 +370,17 @@ dri3_handle_present_event(struct loader_dri3_drawable *draw,
        * checking for wrap.
        */
       if (ce->kind == XCB_PRESENT_COMPLETE_KIND_PIXMAP) {
-         draw->recv_sbc = (draw->send_sbc & 0xffffffff00000000LL) | ce->serial;
-         if (draw->recv_sbc > draw->send_sbc)
-            draw->recv_sbc -= 0x100000000;
+         uint64_t recv_sbc = (draw->send_sbc & 0xffffffff00000000LL) | ce->serial;
+
+         /* Only assume wraparound if that results in exactly the previous
+          * SBC + 1, otherwise ignore received SBC > sent SBC (those are
+          * probably from a previous loader_dri3_drawable instance) to avoid
+          * calculating bogus target MSC values in loader_dri3_swap_buffers_msc
+          */
+         if (recv_sbc <= draw->send_sbc)
+            draw->recv_sbc = recv_sbc;
+         else if (recv_sbc == (draw->recv_sbc + 0x100000001ULL))
+            draw->recv_sbc = recv_sbc - 0x100000000ULL;
 
          /* When moving from flip to copy, we assume that we can allocate in
           * a more optimal way if we don't need to cater for the display
-- 
2.17.0