drm/i915/selftests: Skip using the GPU if wedged

If the GPU is irrecoverably broken, we can not use it to dirty memory
and check for cache coherency with the CPU. All we can do is simply skip
over the GPU subtests and focus on the CPU domains (WC, WB) cache
management.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107127Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180706065332.15214-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/selftests/i915_gem_coherency.c

@@ -239,8 +239,16 @@ static bool always_valid(struct drm_i915_private *i915)
 	return true;
 }
 
+static bool needs_fence_registers(struct drm_i915_private *i915)
+{
+	return !i915_terminally_wedged(&i915->gpu_error);
+}
+
 static bool needs_mi_store_dword(struct drm_i915_private *i915)
 {
+	if (i915_terminally_wedged(&i915->gpu_error))
+		return false;
+
 	return intel_engine_can_store_dword(i915->engine[RCS]);
 }
 
@@ -251,7 +259,7 @@ static const struct igt_coherency_mode {
 	bool (*valid)(struct drm_i915_private *i915);
 } igt_coherency_mode[] = {
 	{ "cpu", cpu_set, cpu_get, always_valid },
-	{ "gtt", gtt_set, gtt_get, always_valid },
+	{ "gtt", gtt_set, gtt_get, needs_fence_registers },
 	{ "wc", wc_set, wc_get, always_valid },
 	{ "gpu", gpu_set, NULL, needs_mi_store_dword },
 	{ },