[PATCH 6/7] drm/i915: Don't break exclusive fence ordering

[Daniel Vetter <daniel.vetter@ffwll.ch>]

There's only one exclusive slot, and we must not break the ordering.

A better fix would be to us a dma_fence_chain or _array like e.g.
amdgpu now uses, but it probably makes sense to lift this into
dma-resv.c code as a proper concept, so that drivers don't have to
hack up their own solution each on their own. Hence go with the simple
fix for now.

Another option is the fence import ioctl from Jason:

https://lore.kernel.org/dri-devel/20210610210925.642582-7-jason@jlekstrand.net/

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 47e07179347a..9d717c8842e2 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1775,6 +1775,7 @@ static int eb_move_to_gpu(struct i915_execbuffer *eb)
 		struct i915_vma *vma = ev->vma;
 		unsigned int flags = ev->flags;
 		struct drm_i915_gem_object *obj = vma->obj;
+		bool async, write;
 
 		assert_vma_held(vma);
 
@@ -1806,7 +1807,10 @@ static int eb_move_to_gpu(struct i915_execbuffer *eb)
 				flags &= ~EXEC_OBJECT_ASYNC;
 		}
 
-		if (err == 0 && !(flags & EXEC_OBJECT_ASYNC)) {
+		async = flags & EXEC_OBJECT_ASYNC;
+		write = flags & EXEC_OBJECT_WRITE;
+
+		if (err == 0 && (!async || write)) {
 			err = i915_request_await_object
 				(eb->request, obj, flags & EXEC_OBJECT_WRITE);
 		}
-- 
2.32.0