nouveau: add an ioctl to report vram usage

This reports the currently used vram allocations.

userspace using this has been proposed for nvk, but
it's a rather trivial uapi addition.
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/nouveau_abi16.c

@@ -267,6 +267,11 @@ nouveau_abi16_ioctl_getparam(ABI16_IOCTL_ARGS)
 	case NOUVEAU_GETPARAM_VRAM_BAR_SIZE:
 		getparam->value = nvkm_device->func->resource_size(nvkm_device, 1);
 		break;
+	case NOUVEAU_GETPARAM_VRAM_USED: {
+		struct ttm_resource_manager *vram_mgr = ttm_manager_type(&drm->ttm.bdev, TTM_PL_VRAM);
+		getparam->value = (u64)ttm_resource_manager_usage(vram_mgr) << PAGE_SHIFT;
+		break;
+	}
 	default:
 		NV_PRINTK(dbg, cli, "unknown parameter %lld\n", getparam->param);
 		return -EINVAL;

include/uapi/drm/nouveau_drm.h

@@ -61,6 +61,13 @@ extern "C" {
  */
 #define NOUVEAU_GETPARAM_VRAM_BAR_SIZE 18
 
+/*
+ * NOUVEAU_GETPARAM_VRAM_USED
+ *
+ * Get remaining VRAM size.
+ */
+#define NOUVEAU_GETPARAM_VRAM_USED 19
+
 struct drm_nouveau_getparam {
 	__u64 param;
 	__u64 value;