[PATCH 12/18] drm/i915/guc: Ensure request ordering via completion fences

[Matthew Brost]

If two requests are on the same ring, they are explicitly ordered by the
HW. So, a submission fence is sufficient to ensure ordering when using
the new GuC submission interface. Conversely, if two requests share a
timeline and are on the same physical engine but different context this
doesn't ensure ordering on the new GuC submission interface. So, a
completion fence needs to be used to ensure ordering.

v2:
 (Daniele)
  - Don't delete spin lock
v3:
 (Daniele)
  - Delete forward dec

Signed-off-by: John Harrison <john.c.harri...@intel.com>
Signed-off-by: Matthew Brost <matthew.br...@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospu...@intel.com>
---
 drivers/gpu/drm/i915/i915_request.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_request.c 
b/drivers/gpu/drm/i915/i915_request.c
index ef26724fe980..c55dea0edb09 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -432,6 +432,7 @@ void i915_request_retire_upto(struct i915_request *rq)
 
        do {
                tmp = list_first_entry(&tl->requests, typeof(*tmp), link);
+               GEM_BUG_ON(!i915_request_completed(tmp));
        } while (i915_request_retire(tmp) && tmp != rq);
 }
 
@@ -1463,7 +1464,8 @@ i915_request_await_request(struct i915_request *to, 
struct i915_request *from)
                        return ret;
        }
 
-       if (is_power_of_2(to->execution_mask | READ_ONCE(from->execution_mask)))
+       if (!intel_engine_uses_guc(to->engine) &&
+           is_power_of_2(to->execution_mask | READ_ONCE(from->execution_mask)))
                ret = await_request_submit(to, from);
        else
                ret = emit_semaphore_wait(to, from, I915_FENCE_GFP);
@@ -1622,6 +1624,8 @@ __i915_request_add_to_timeline(struct i915_request *rq)
        prev = to_request(__i915_active_fence_set(&timeline->last_request,
                                                  &rq->fence));
        if (prev && !__i915_request_is_complete(prev)) {
+               bool uses_guc = intel_engine_uses_guc(rq->engine);
+
                /*
                 * The requests are supposed to be kept in order. However,
                 * we need to be wary in case the timeline->last_request
@@ -1632,7 +1636,9 @@ __i915_request_add_to_timeline(struct i915_request *rq)
                           i915_seqno_passed(prev->fence.seqno,
                                             rq->fence.seqno));
 
-               if (is_power_of_2(READ_ONCE(prev->engine)->mask | 
rq->engine->mask))
+               if ((!uses_guc &&
+                    is_power_of_2(READ_ONCE(prev->engine)->mask | 
rq->engine->mask)) ||
+                   (uses_guc && prev->context == rq->context))
                        i915_sw_fence_await_sw_fence(&rq->submit,
                                                     &prev->submit,
                                                     &rq->submitq);
-- 
2.28.0