drm/i915: Missed interrupt simulation is no more, tell the world

Using the guc, we cannot disable the user interrupt generation as we use
it for driving submission. And from Icelake, we no longer have the
ability to individually mask interrupt generation from each engine,
disabling our ability to fake missed interrupts.

In both cases, report back to userspace that the missed interrupt
generator is no longer available.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180907112856.28242-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -4117,6 +4117,17 @@ i915_ring_test_irq_set(void *data, u64 val)
 {
 	struct drm_i915_private *i915 = data;
 
+	/* GuC keeps the user interrupt permanently enabled for submission */
+	if (USES_GUC_SUBMISSION(i915))
+		return -ENODEV;
+
+	/*
+	 * From icl, we can no longer individually mask interrupt generation
+	 * from each engine.
+	 */
+	if (INTEL_GEN(i915) >= 11)
+		return -ENODEV;
+
 	val &= INTEL_INFO(i915)->ring_mask;
 	DRM_DEBUG_DRIVER("Masking interrupts on rings 0x%08llx\n", val);