From bcd4d0b591146f9234d5977ee66a641622733862 Mon Sep 17 00:00:00 2001
From: jsg <jsg@openbsd.org>
Date: Fri, 16 Sep 2022 01:48:07 +0000
Subject: [PATCH] mask non-chain fence sequence numbers to 32-bit for
 comparisons

Most of drm uses 32-bit sequence numbers in fences.
dma-fence-chain opts into 64-bit comparisons.

Wrapping is handled like i915_seqno_passed() except that if the sequence
numbers are the same one is not considered later than the other.
---
 sys/dev/pci/drm/drm_linux.c               |  5 +++--
 sys/dev/pci/drm/include/linux/dma-fence.h | 23 ++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/sys/dev/pci/drm/drm_linux.c b/sys/dev/pci/drm/drm_linux.c
index 16ff64f1824..2b975cda9fb 100644
--- a/sys/dev/pci/drm/drm_linux.c
+++ b/sys/dev/pci/drm/drm_linux.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: drm_linux.c,v 1.93 2022/06/20 01:39:44 visa Exp $	*/
+/*	$OpenBSD: drm_linux.c,v 1.94 2022/09/16 01:48:07 jsg Exp $	*/
 /*
  * Copyright (c) 2013 Jonathan Gray <jsg@openbsd.org>
  * Copyright (c) 2015, 2016 Mark Kettenis <kettenis@openbsd.org>
@@ -2084,7 +2084,7 @@ dma_fence_chain_init(struct dma_fence_chain *chain, struct dma_fence *prev,
 
 	/* if prev is a chain */
 	if (to_dma_fence_chain(prev) != NULL) {
-		if (seqno > prev->seqno) {
+		if (__dma_fence_is_later(seqno, prev->seqno, prev->ops)) {
 			chain->prev_seqno = prev->seqno;
 			context = prev->context;
 		} else {
@@ -2240,6 +2240,7 @@ const struct dma_fence_ops dma_fence_chain_ops = {
 	.enable_signaling = dma_fence_chain_enable_signaling,
 	.signaled = dma_fence_chain_signaled,
 	.release = dma_fence_chain_release,
+	.use_64bit_seqno = true,
 };
 
 int
diff --git a/sys/dev/pci/drm/include/linux/dma-fence.h b/sys/dev/pci/drm/include/linux/dma-fence.h
index 39220dc54f5..06d2cb644a3 100644
--- a/sys/dev/pci/drm/include/linux/dma-fence.h
+++ b/sys/dev/pci/drm/include/linux/dma-fence.h
@@ -41,6 +41,7 @@ struct dma_fence_ops {
 	bool (*signaled)(struct dma_fence *);
 	long (*wait)(struct dma_fence *, bool, long);
 	void (*release)(struct dma_fence *);
+	bool use_64bit_seqno;
 };
 
 struct dma_fence_cb;
@@ -84,10 +85,30 @@ dma_fence_free(struct dma_fence *fence)
 	free(fence, M_DRM, 0);
 }
 
+/*
+ * is a later than b
+ * if a and b are the same, should return false to avoid unwanted work
+ */
+static inline bool
+__dma_fence_is_later(uint64_t a, uint64_t b, const struct dma_fence_ops *ops)
+{
+	uint32_t al, bl;
+
+	if (ops->use_64bit_seqno)
+		return a > b;
+
+	al = a & 0xffffffff;
+	bl = b & 0xffffffff;
+
+	return (int)(al - bl) > 0;
+}
+
 static inline bool
 dma_fence_is_later(struct dma_fence *a, struct dma_fence *b)
 {
-	return (a->seqno > b->seqno);
+	if (a->context != b->context)
+		return false;
+	return __dma_fence_is_later(a->seqno, b->seqno, a->ops);
 }
 
 static inline void
-- 
2.20.1