drm/vmwgfx: Do not allow invalid bpp's for dumb buffers

Dumb buffers allow a very limited set of formats. Basically everything
apart from 1, 2 and 4 is expected to return an error. Make vmwgfx
follow those guidelines.

This fixes igt's dumb_buffer invalid_bpp test on vmwgfx.
Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Reviewed-by: Maaz Mombasawala <mombasawalam@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221022040236.616490-13-zack@kde.org

drivers/gpu/drm/vmwgfx/vmwgfx_bo.c

@@ -807,9 +807,23 @@ int vmw_dumb_create(struct drm_file *file_priv,
 {
 	struct vmw_private *dev_priv = vmw_priv(dev);
 	struct vmw_buffer_object *vbo;
+	int cpp = DIV_ROUND_UP(args->bpp, 8);
 	int ret;
 
-	args->pitch = args->width * ((args->bpp + 7) / 8);
+	switch (cpp) {
+	case 1: /* DRM_FORMAT_C8 */
+	case 2: /* DRM_FORMAT_RGB565 */
+	case 4: /* DRM_FORMAT_XRGB8888 */
+		break;
+	default:
+		/*
+		 * Dumb buffers don't allow anything else.
+		 * This is tested via IGT's dumb_buffers
+		 */
+		return -EINVAL;
+	}
+
+	args->pitch = args->width * cpp;
 	args->size = ALIGN(args->pitch * args->height, PAGE_SIZE);
 
 	ret = vmw_gem_object_create_with_handle(dev_priv, file_priv,