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

[Chris Wilson]

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.krzyszto...@linux.intel.com>
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Janusz Krzysztofik <janusz.krzyszto...@linux.intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospu...@intel.com>
Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospu...@intel.com>
---
 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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