drm/i915/gt: Ignore stale context state upon resume

We leave the kernel_context on the HW as we suspend (and while idle).
There is no guarantee that is complete in memory, so we try to inhibit
restoration from the kernel_context. Reinforce the inhibition by
scrubbing the context.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200102131707.1463945-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -2602,6 +2602,9 @@ static int execlists_context_alloc(struct intel_context *ce)
 
 static void execlists_context_reset(struct intel_context *ce)
 {
+	CE_TRACE(ce, "reset\n");
+	GEM_BUG_ON(!intel_context_is_pinned(ce));
+
 	/*
 	 * Because we emit WA_TAIL_DWORDS there may be a disparity
 	 * between our bookkeeping in ce->ring->head and ce->ring->tail and
@@ -2618,8 +2621,14 @@ static void execlists_context_reset(struct intel_context *ce)
 	 * So to avoid that we reset the context images upon resume. For
 	 * simplicity, we just zero everything out.
 	 */
-	intel_ring_reset(ce->ring, 0);
+	intel_ring_reset(ce->ring, ce->ring->emit);
+
+	/* Scrub away the garbage */
+	execlists_init_reg_state(ce->lrc_reg_state,
+				 ce, ce->engine, ce->ring, true);
 	__execlists_update_reg_state(ce, ce->engine);
+
+	ce->lrc_desc |= CTX_DESC_FORCE_RESTORE;
 }
 
 static const struct intel_context_ops execlists_context_ops = {

drivers/gpu/drm/i915/gt/intel_ring_submission.c

@@ -1347,7 +1347,7 @@ static int ring_context_pin(struct intel_context *ce)
 
 static void ring_context_reset(struct intel_context *ce)
 {
-	intel_ring_reset(ce->ring, 0);
+	intel_ring_reset(ce->ring, ce->ring->emit);
 }
 
 static const struct intel_context_ops ring_context_ops = {