diff --git a/crates/vhost-device-gpio/README.md b/crates/vhost-device-gpio/README.md
index c063698..0daa190 100644
--- a/crates/vhost-device-gpio/README.md
+++ b/crates/vhost-device-gpio/README.md
@@ -43,6 +43,28 @@ Examples section below.
   --socket-count. For example, the GPIO device 0 will be allocated to the guest
   with "<socket-path>0" path.
 
+## MockGpioDevice support
+
+As connecting VM guests to random GPIO pins on your host is generally
+asking for trouble you can enable the "mock_gpio" feature in your build:
+
+    cargo build --features "mock_gpio"
+
+You can then enable simulated GPIOs using the 's' prefix:
+
+    --device-list s4,s8
+
+Which will create two gpio devices, the first with 4 pins and the
+second with 8. By default updates are display via env logger:
+
+    vhost-device-gpio -s /tmp/vus.sock -c 1 -l s4
+    [2023-09-14T14:15:14Z INFO  vhost_device_gpio::mock_gpio] gpio dummy0 set value to 1
+    [2023-09-14T14:15:14Z INFO  vhost_device_gpio::mock_gpio] gpio dummy0 set direction to 1
+    [2023-09-14T14:15:14Z INFO  vhost_device_gpio::mock_gpio] gpio dummy0 set direction to 0
+    [2023-09-14T14:15:19Z INFO  vhost_device_gpio::mock_gpio] gpio dummy1 set value to 1
+    [2023-09-14T14:15:19Z INFO  vhost_device_gpio::mock_gpio] gpio dummy1 set direction to 1
+    [2023-09-14T14:15:19Z INFO  vhost_device_gpio::mock_gpio] gpio dummy1 set direction to 0
+
 ## Examples
 
 The daemon should be started first:
diff --git a/crates/vhost-device-rng/CHANGELOG.md b/crates/vhost-device-rng/CHANGELOG.md
index 51d3f04..362be20 100644
--- a/crates/vhost-device-rng/CHANGELOG.md
+++ b/crates/vhost-device-rng/CHANGELOG.md
@@ -3,6 +3,8 @@
 
 ### Added
 
+  - optional "mock_gpio" feature for testing
+
 ### Changed
 
 ### Fixed