drm/i915: announce to userspace that the bsd ring is coherent

Otherwise we can't really fix the abi-braindeadness of forcing
libva to manually wait for rendering when switching rings. Which
in turn makes implementing hw semaphores a pointless exercise
(at least for ironlake).

[Also added the relaxed fencing param to explain the jump in
numbering - relaxed fencing is in -next.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_dma.c

@@ -767,6 +767,9 @@ static int i915_getparam(struct drm_device *dev, void *data,
 	case I915_PARAM_HAS_BLT:
 		value = HAS_BLT(dev);
 		break;
+	case I915_PARAM_HAS_COHERENT_RINGS:
+		value = 1;
+		break;
 	default:
 		DRM_DEBUG_DRIVER("Unknown parameter %d\n",
 				 param->param);

include/drm/i915_drm.h

@@ -287,6 +287,8 @@ typedef struct drm_i915_irq_wait {
 #define I915_PARAM_HAS_EXECBUF2          9
 #define I915_PARAM_HAS_BSD		 10
 #define I915_PARAM_HAS_BLT		 11
+#define I915_PARAM_HAS_RELAXED_FENCING	 12
+#define I915_PARAM_HAS_COHERENT_RINGS	 13
 
 typedef struct drm_i915_getparam {
 	int param;