[src/trunk]: src/sys/external/bsd/drm2/linux drm: Use atomic_load_consume/rel...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/5481929ce982
branches:  trunk
changeset: 1028991:5481929ce982
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sun Dec 19 12:39:40 2021 +0000

description:
drm: Use atomic_load_consume/relaxed to simplify code.

diffstat:

 sys/external/bsd/drm2/linux/linux_dma_fence.c |  25 +++++++++----------------
 1 files changed, 9 insertions(+), 16 deletions(-)

diffs (57 lines):

diff -r ca70978b2cae -r 5481929ce982 sys/external/bsd/drm2/linux/linux_dma_fence.c
--- a/sys/external/bsd/drm2/linux/linux_dma_fence.c     Sun Dec 19 12:39:32 2021 +0000
+++ b/sys/external/bsd/drm2/linux/linux_dma_fence.c     Sun Dec 19 12:39:40 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: linux_dma_fence.c,v 1.38 2021/12/19 12:39:25 riastradh Exp $   */
+/*     $NetBSD: linux_dma_fence.c,v 1.39 2021/12/19 12:39:40 riastradh Exp $   */
 
 /*-
  * Copyright (c) 2018 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: linux_dma_fence.c,v 1.38 2021/12/19 12:39:25 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: linux_dma_fence.c,v 1.39 2021/12/19 12:39:40 riastradh Exp $");
 
 #include <sys/atomic.h>
 #include <sys/condvar.h>
@@ -394,21 +394,16 @@
 struct dma_fence *
 dma_fence_get_rcu_safe(struct dma_fence *volatile const *fencep)
 {
-       struct dma_fence *fence, *fence0;
+       struct dma_fence *fence;
 
 retry:
-       fence = *fencep;
-
-       /* Load fence only once.  */
-       __insn_barrier();
-
-       /* If there's nothing there, give up.  */
-       if (fence == NULL)
+       /*
+        * Load the fence, ensuring we observe the fully initialized
+        * content.
+        */
+       if ((fence = atomic_load_consume(fencep)) == NULL)
                return NULL;
 
-       /* Make sure we don't load stale fence guts.  */
-       membar_datadep_consumer();
-
        /* Try to acquire a reference.  If we can't, try again.  */
        if (!dma_fence_get_rcu(fence))
                goto retry;
@@ -417,9 +412,7 @@
         * Confirm that it's still the same fence.  If not, release it
         * and retry.
         */
-       fence0 = *fencep;
-       __insn_barrier();
-       if (fence != fence0) {
+       if (fence != atomic_load_relaxed(fencep)) {
                dma_fence_put(fence);
                goto retry;
        }