drm/i915: Restore engine->submit_request before unwedging

When we wedge the device, we override engine->submit_request with a nop
to ensure that all in-flight requests are marked in error. However, igt
would like to unwedge the device to test -EIO handling. This requires us
to flush those in-flight requests and restore the original
engine->submit_request.

v2: Use a vfunc to unify enabling request submission to engines
v3: Split new vfunc to a separate patch.
v4: Make the wait interruptible -- the third party fences we wait upon
may be indefinitely broken, so allow the reset to be aborted.

Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests")
Testcase: igt/gem_eio
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> #v3
Link: http://patchwork.freedesktop.org/patch/msgid/20170316171305.12972-3-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index be3c812..03d9e45 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1821,7 +1821,9 @@ void i915_reset(struct drm_i915_private *dev_priv)
 		return;
 
 	/* Clear any previous failed attempts at recovery. Time to try again. */
-	__clear_bit(I915_WEDGED, &error->flags);
+	if (!i915_gem_unset_wedged(dev_priv))
+		goto wakeup;
+
 	error->reset_count++;
 
 	pr_notice("drm/i915: Resetting chip after gpu hang\n");
@@ -1867,17 +1869,18 @@ void i915_reset(struct drm_i915_private *dev_priv)
 
 	i915_queue_hangcheck(dev_priv);
 
-wakeup:
+finish:
 	i915_gem_reset_finish(dev_priv);
 	enable_irq(dev_priv->drm.irq);
 
+wakeup:
 	clear_bit(I915_RESET_HANDOFF, &error->flags);
 	wake_up_bit(&error->flags, I915_RESET_HANDOFF);
 	return;
 
 error:
 	i915_gem_set_wedged(dev_priv);
-	goto wakeup;
+	goto finish;
 }
 
 static int i915_pm_suspend(struct device *kdev)