commit 5af05fefb5be51d42effc4f802b6d806fbda34eb
author Michel Thierry <michel.thierry@intel.com> Fri Sep 04 12:59:15 2015 +0100
committer Daniel Vetter <daniel.vetter@ffwll.ch> Mon Sep 14 10:25:01 2015 +0200
tree 581465d8cb3aed92f2cdca5deb56b0643ec86e43
parent ec72d5884c6a3cf4f27b52da51654a472b919545

drm/i915/lrc: Prevent preemption when lite-restore is disabled

When WaEnableForceRestoreInCtxtDescForVCS is required, it is only
safe to send new contexts if the last reported event is "active to
idle". Otherwise the same context can fully preempt itself because
lite-restore is disabled.

Testcase: igt/gem_concurrent_blit
Reported-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Tested-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index d8b605f..c3fca4b 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -277,10 +277,18 @@
 	return lrca >> 12;
 }
 
+static bool disable_lite_restore_wa(struct intel_engine_cs *ring)
+{
+	struct drm_device *dev = ring->dev;
+
+	return ((IS_SKYLAKE(dev) && INTEL_REVID(dev) <= SKL_REVID_B0) ||
+		(IS_BROXTON(dev) && INTEL_REVID(dev) == BXT_REVID_A0)) &&
+	       (ring->id == VCS || ring->id == VCS2);
+}
+
 uint64_t intel_lr_context_descriptor(struct intel_context *ctx,
 				     struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
 	struct drm_i915_gem_object *ctx_obj = ctx->engine[ring->id].state;
 	uint64_t desc;
 	uint64_t lrca = i915_gem_obj_ggtt_offset(ctx_obj) +
@@ -302,9 +310,7 @@
 
 	/* WaEnableForceRestoreInCtxtDescForVCS:skl */
 	/* WaEnableForceRestoreInCtxtDescForVCS:bxt */
-	if (((IS_SKYLAKE(dev) && INTEL_REVID(dev) <= SKL_REVID_B0) ||
-	     (IS_BROXTON(dev) && INTEL_REVID(dev) == BXT_REVID_A0)) &&
-	    (ring->id == VCS || ring->id == VCS2))
+	if (disable_lite_restore_wa(ring))
 		desc |= GEN8_CTX_FORCE_RESTORE;
 
 	return desc;
@@ -495,7 +501,7 @@
 	u32 status_pointer;
 	u8 read_pointer;
 	u8 write_pointer;
-	u32 status;
+	u32 status = 0;
 	u32 status_id;
 	u32 submit_contexts = 0;
 
@@ -533,8 +539,14 @@
 		}
 	}
 
-	if (submit_contexts != 0)
+	if (disable_lite_restore_wa(ring)) {
+		/* Prevent a ctx to preempt itself */
+		if ((status & GEN8_CTX_STATUS_ACTIVE_IDLE) &&
+		    (submit_contexts != 0))
+			execlists_context_unqueue(ring);
+	} else if (submit_contexts != 0) {
 		execlists_context_unqueue(ring);
+	}
 
 	spin_unlock(&ring->execlist_lock);