USB: make the usbfs memory limit configurable

The 16-MB global limit on memory used by usbfs isn't suitable for all
people.  It's a reasonable default, but there are applications
(especially for SuperSpeed devices) that need a lot more.

This patch (as1498) creates a writable module parameter for usbcore to
control the global limit.  The default is still 16 MB, but users can
change it at runtime, even after usbcore has been loaded.  As a
special case, setting the value to 0 is treated the same as the hard
limit of 2047 MB.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a0c5c5f..72c68bb 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2632,6 +2632,10 @@
 			[USB] Start with the old device initialization
 			scheme (default 0 = off).
 
+	usbcore.usbfs_memory_mb=
+			[USB] Memory limit (in MB) for buffers allocated by
+			usbfs (default = 16, 0 = max = 2047).
+
 	usbcore.use_both_schemes=
 			[USB] Try the other device initialization scheme
 			if the first one fails (default 1 = enabled).