[PATCH] drm/i915/gt: Only unwedge if we can reset first

[Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>]

Unwedging the GPU requires a successful GPU reset before we restore the
default submission, or else we may see residual context switch events
that we were not expecting.

v2: Pull in the special-case reset_clobbers_display, and explain why it
should be safe in the context of unwedging.

Reported-by: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
---
 drivers/gpu/drm/i915/gt/intel_reset.c | 30 ++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
index ee52947eb31d..d3b1cdafd4c2 100644
--- a/drivers/gpu/drm/i915/gt/intel_reset.c
+++ b/drivers/gpu/drm/i915/gt/intel_reset.c
@@ -7,6 +7,7 @@
 #include <linux/sched/mm.h>
 #include <linux/stop_machine.h>
 
+#include "display/intel_display.h"
 #include "display/intel_display_types.h"
 #include "display/intel_overlay.h"
 
@@ -729,6 +730,28 @@ static void nop_submit_request(struct i915_request *request)
 	intel_engine_queue_breadcrumbs(engine);
 }
 
+static bool reset_clobbers_display(struct drm_i915_private *i915)
+{
+	struct intel_crtc *crtc;
+
+	if (!INTEL_INFO(i915)->gpu_reset_clobbers_display)
+		return false;
+
+	/*
+	 * While this appears racy, we should only be inspecting the display
+	 * state at runtime from inside a GPU reset, which will be serialized
+	 * with modesets on affected machines. For a full device reset,
+	 * we should already have cleared the active CRTC state in
+	 * intel_prepare_reset().
+	 */
+	for_each_intel_crtc(&i915->drm, crtc) {
+		if (crtc->active)
+			return true;
+	}
+
+	return false;
+}
+
 static void __intel_gt_set_wedged(struct intel_gt *gt)
 {
 	struct intel_engine_cs *engine;
@@ -793,6 +816,7 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
 	struct intel_gt_timelines *timelines = &gt->timelines;
 	struct intel_timeline *tl;
 	unsigned long flags;
+	bool ok;
 
 	if (!test_bit(I915_WEDGED, &gt->reset.flags))
 		return true;
@@ -838,7 +862,11 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
 	}
 	spin_unlock_irqrestore(&timelines->lock, flags);
 
-	intel_gt_sanitize(gt, false);
+	ok = false;
+	if (!reset_clobbers_display(gt->i915))
+		ok = __intel_gt_reset(gt, ALL_ENGINES) == 0;
+	if (!ok)
+		return false;
 
 	/*
 	 * Undo nop_submit_request. We prevent all new i915 requests from
-- 
2.23.0

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