drm/i915: Make closing request flush mandatory

For symmetry, simplicity and ensuring the request is always truly idle
upon its completion, always emit the closing flush prior to emitting the
request breadcrumb. Previously, we would only emit the flush if we had
started a user batch, but this just leaves all the other paths open to
speculation (do they affect the GPU caches or not?) With mm switching, a
key requirement is that the GPU is flushed and invalidated before hand,
so for absolute safety, we want that closing flush be mandatory.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180612105135.4459-1-chris@chris-wilson.co.uk

1 files changed, 2 insertions, 16 deletions

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 9092f5464c24..e1dbb544046f 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -1018,14 +1018,13 @@ i915_request_await_object(struct i915_request *to,
  * request is not being tracked for completion but the work itself is
  * going to happen on the hardware. This would be a Bad Thing(tm).
  */
-void __i915_request_add(struct i915_request *request, bool flush_caches)
+void i915_request_add(struct i915_request *request)
 {
         struct intel_engine_cs *engine = request->engine;
         struct i915_timeline *timeline = request->timeline;
         struct intel_ring *ring = request->ring;
         struct i915_request *prev;
         u32 *cs;
-        int err;
 
         GEM_TRACE("%s fence %llx:%d\n",
                   engine->name, request->fence.context, request->fence.seqno);
@@ -1046,20 +1045,7 @@ void __i915_request_add(struct i915_request *request, bool flush_caches)
          * know that it is time to use that space up.
          */
         request->reserved_space = 0;
-
-        /*
-         * Emit any outstanding flushes - execbuf can fail to emit the flush
-         * after having emitted the batchbuffer command. Hence we need to fix
-         * things up similar to emitting the lazy request. The difference here
-         * is that the flush _must_ happen before the next request, no matter
-         * what.
-         */
-        if (flush_caches) {
-                err = engine->emit_flush(request, EMIT_FLUSH);
-
-                /* Not allowed to fail! */
-                WARN(err, "engine->emit_flush() failed: %d!\n", err);
-        }
+        engine->emit_flush(request, EMIT_FLUSH);
 
         /*
          * Record the position of the start of the breadcrumb so that