document firmware support
diff --git a/docs/mdev.txt b/docs/mdev.txt
index 51c3f0e..0b2c37d 100644
--- a/docs/mdev.txt
+++ b/docs/mdev.txt
@@ -66,3 +66,15 @@
For your convenience, the shell env var $MDEV is set to the device name. So if
the device 'hdc' was matched, MDEV would be set to "hdc".
+
+----------
+ FIRMWARE
+----------
+
+Some kernel device drivers need to request firmware at runtime in order to
+properly initialize a device. Place all such firmware files into the
+/lib/firmware/ directory. At runtime, the kernel will invoke mdev with the
+filename of the firmware which mdev will load out of /lib/firmware/ and into
+the kernel via the sysfs interface. The exact filename is hardcoded in the
+kernel, so look there if you need to want to know what to name the file in
+userspace.