diff --git a/Documentation/sound/alsa/ALSA-Configuration.txt b/Documentation/sound/alsa/ALSA-Configuration.txt
index c540637..c83fd7b 100644
--- a/Documentation/sound/alsa/ALSA-Configuration.txt
+++ b/Documentation/sound/alsa/ALSA-Configuration.txt
@@ -482,6 +482,9 @@
 
     reference_rate	- reference sample rate, 44100 or 48000 (default)
     multiple		- multiple to ref. sample rate, 1 or 2 (default)
+    subsystem		- override the PCI SSID for probing; the value
+			  consists of SSVID << 16 | SSDID.  The default is
+			  zero, which means no override.
 
     This module supports multiple cards.