drm/i915: Wait for a moment before forcibly resetting the device

During igt, we ask to reset the device if any requests are still
outstanding at the end of a test, as this quickly kills off any
erroneous hanging request streams that may escape a test. However, since
it may take the device a few milliseconds to flush itself after the end
of a normal test, *cough* guc *cough*, we may accidentally tell the
device to reset itself after it idles. If we wait a moment, our usual
I915_IDLE_ENGINES_TIMEOUT of 200ms (seems a bit high, but still better
than umpteen hangchecks!), we can differentiate better between a stuck
engine and a healthy one, and so avoid prematurely forcing the reset and
any extra complications that may entail.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190128010245.20148-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -4050,7 +4050,8 @@ i915_drop_caches_set(void *data, u64 val)
 		  val, val & DROP_ALL);
 	wakeref = intel_runtime_pm_get(i915);
 
-	if (val & DROP_RESET_ACTIVE && !intel_engines_are_idle(i915))
+	if (val & DROP_RESET_ACTIVE &&
+	    wait_for(intel_engines_are_idle(i915), I915_IDLE_ENGINES_TIMEOUT))
 		i915_gem_set_wedged(i915);
 
 	/* No need to check and wait for gpu resets, only libdrm auto-restarts