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, 1 insertions, 8 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index b2c7ac1b074d..ef6ea4bcd773 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -700,14 +700,7 @@ int i915_gem_switch_to_kernel_context(struct drm_i915_private *i915)
 			i915_timeline_sync_set(rq->timeline, &prev->fence);
 		}
 
-		/*
-		 * Force a flush after the switch to ensure that all rendering
-		 * and operations prior to switching to the kernel context hits
-		 * memory. This should be guaranteed by the previous request,
-		 * but an extra layer of paranoia before we declare the system
-		 * idle (on suspend etc) is advisable!
-		 */
-		__i915_request_add(rq, true);
+		i915_request_add(rq);
 	}
 
 	return 0;