[Intel-gfx] [RFC PATCH] drm/i915/debugfs: Only wedge if we have reset available

[Janusz Krzysztofik]

If we process DROP_RESET_ACTIVE and cancel all outstanding requests by
forcing a GPU reset on a hardware with reset capabilities disabled or
not supported, we certainly end up with a terminally wedged GPU,
impossible to recover.  That's probably not what we want.

Before setting the GPU wedged, verify if we have GPU reset available
and fail with -EBUSY if not.

Suggested-by: Petri Latvala <petri.latvala at intel.com>
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik at linux.intel.com>
Cc: Michał Wajdeczko <michal.wajdeczko at intel.com>
Cc: Michał Winiarski <michal.winiarski at intel.com>
Cc: Piotr Piórkowski <piotr.piorkowski at intel.com>
Cc: Tomasz Lis <tomasz.lis at intel.com>
Cc: Petri Latvala <petri.latvala at intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Martin Peres <martin.peres at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index fec9fb7cc384..0774ca6e2a05 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -3627,8 +3627,17 @@ i915_drop_caches_set(void *data, u64 val)
 
 	if (val & DROP_RESET_ACTIVE &&
 	    wait_for(intel_engines_are_idle(&i915->gt),
-		     I915_IDLE_ENGINES_TIMEOUT))
+		     I915_IDLE_ENGINES_TIMEOUT)) {
+		/*
+		 * Only wedge if reset is supported and not disabled, otherwise
+		 * we certainly end up with the GPU terminally wedged.  Inform
+		 * userspace about the problem instead.
+		 */
+		if (!intel_has_gpu_reset(&i915->gt))
+			return -EBUSY;
+
 		intel_gt_set_wedged(&i915->gt);
+	}
 
 	/* No need to check and wait for gpu resets, only libdrm auto-restarts
 	 * on ioctls on -EAGAIN. */
-- 
2.21.0