drm/i915: expose _SLICE_MASK GETPARM

Enables userspace to determine the maximum number of slices that can
be enabled on the device and also know what specific slices can be
enabled. This information is required, for example, to be able to
analyse some OA counter reports where the counter configuration
depends on the HW slice configuration.
Signed-off-by: Robert Bragg <robert@sixbynine.org>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>

drivers/gpu/drm/i915/i915_drv.c

@@ -374,6 +374,11 @@ static int i915_getparam(struct drm_device *dev, void *data,
 		 */
 		value = 1;
 		break;
+	case I915_PARAM_SLICE_MASK:
+		value = INTEL_INFO(dev_priv)->sseu.slice_mask;
+		if (!value)
+			return -ENODEV;
+		break;
 	default:
 		DRM_DEBUG("Unknown parameter %d\n", param->param);
 		return -EINVAL;

include/uapi/drm/i915_drm.h

@@ -418,6 +418,9 @@ typedef struct drm_i915_irq_wait {
  */
 #define I915_PARAM_HAS_EXEC_CAPTURE	 45
 
+/* Query the mask of slices available for this system */
+#define I915_PARAM_SLICE_MASK		 46
+
 typedef struct drm_i915_getparam {
 	__s32 param;
 	/*