drm/virtio: make resource id workaround runtime switchable.

Also update the comment with a reference to the virglrenderer fix.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20190822102614.18164-1-kraxel@redhat.com

drivers/gpu/drm/virtio/virtgpu_object.c

@@ -27,34 +27,38 @@
 
 #include "virtgpu_drv.h"
 
+static int virtio_gpu_virglrenderer_workaround = 1;
+module_param_named(virglhack, virtio_gpu_virglrenderer_workaround, int, 0400);
+
 static int virtio_gpu_resource_id_get(struct virtio_gpu_device *vgdev,
 				       uint32_t *resid)
 {
-#if 0
-	int handle = ida_alloc(&vgdev->resource_ida, GFP_KERNEL);
-
-	if (handle < 0)
-		return handle;
-#else
-	static int handle;
-
+	if (virtio_gpu_virglrenderer_workaround) {
 		/*
-	 * FIXME: dirty hack to avoid re-using IDs, virglrenderer
-	 * can't deal with that.  Needs fixing in virglrenderer, also
-	 * should figure a better way to handle that in the guest.
+		 * Hack to avoid re-using resource IDs.
+		 *
+		 * virglrenderer versions up to (and including) 0.7.0
+		 * can't deal with that.  virglrenderer commit
+		 * "f91a9dd35715 Fix unlinking resources from hash
+		 * table." (Feb 2019) fixes the bug.
 		 */
+		static int handle;
 		handle++;
-#endif
-
 		*resid = handle + 1;
+	} else {
+		int handle = ida_alloc(&vgdev->resource_ida, GFP_KERNEL);
+		if (handle < 0)
+			return handle;
+		*resid = handle + 1;
+	}
 	return 0;
 }
 
 static void virtio_gpu_resource_id_put(struct virtio_gpu_device *vgdev, uint32_t id)
 {
-#if 0
+	if (!virtio_gpu_virglrenderer_workaround) {
 		ida_free(&vgdev->resource_ida, id - 1);
-#endif
+	}
 }
 
 static void virtio_gpu_ttm_bo_destroy(struct ttm_buffer_object *tbo)