drm/i915: Prevent use of global_seqno=0

We are not allowed to assign rq->global_seqno=0 as it has a special
meaning of "inactive" (not executing on HW).

Fixes: 6faf5916e6be ("drm/i915: Remove HW semaphores for gen7 inter-engine synchronisation")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190119143024.26971-1-chris@chris-wilson.co.uk

1 files changed, 8 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 33eb9df0dd0e..c7ce27785cda 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -343,6 +343,13 @@ static void move_to_timeline(struct i915_request *request,
         spin_unlock(&request->timeline->lock);
 }
 
+static u32 next_global_seqno(struct i915_timeline *tl)
+{
+        if (!++tl->seqno)
+                ++tl->seqno;
+        return tl->seqno;
+}
+
 void __i915_request_submit(struct i915_request *request)
 {
         struct intel_engine_cs *engine = request->engine;
@@ -359,7 +366,7 @@ void __i915_request_submit(struct i915_request *request)
 
         GEM_BUG_ON(request->global_seqno);
 
-        seqno = timeline_get_seqno(&engine->timeline);
+        seqno = next_global_seqno(&engine->timeline);
         GEM_BUG_ON(!seqno);
         GEM_BUG_ON(intel_engine_signaled(engine, seqno));