doc: kernel-parameters.txt: Add ide-generic.probe-mask

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
[ jc: wording tweaked slightly ]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/kernel-parameters.txt

@@ -1303,6 +1303,18 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			.cdrom .chs .ignore_cable are additional options
 			See Documentation/ide/ide.txt.
 
+	ide-generic.probe-mask= [HW] (E)IDE subsystem
+			Format: <int>
+			Probe mask for legacy ISA IDE ports.  Depending on
+			platform up to 6 ports are supported, enabled by
+			setting corresponding bits in the mask to 1.  The
+			default value is 0x0, which has a special meaning.
+			On systems that have PCI, it triggers scanning the
+			PCI bus for the first and the second port, which
+			are then probed.  On systems without PCI the value
+			of 0x0 enables probing the two first ports as if it
+			was 0x3.
+
 	ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
 			Claim all unknown PCI IDE storage controllers.