USB: fix comment about endianness of descriptors

This patch fixes a comment and clarifies the documentation about the
endianness of descriptors. The current policy is that descriptors will
be little-endian at the API even on big-endian systems; however the
/proc/bus/usb API predates this policy and presents descriptors with
some multibyte fields byte-swapped.

Signed-off-by: Phil Endecott <usb_endian_patch@chezphil.org>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/Documentation/usb/proc_usb_info.txt b/Documentation/usb/proc_usb_info.txt
index 077e903..fafcd47 100644 (file)
--- a/Documentation/usb/proc_usb_info.txt
+++ b/Documentation/usb/proc_usb_info.txt
@@ -49,8 +49,10 @@ it and 002/048 sometime later.
 
 These files can be read as binary data.  The binary data consists
 of first the device descriptor, then the descriptors for each
-configuration of the device.  That information is also shown in
-text form by the /proc/bus/usb/devices file, described later.
+configuration of the device.  Multi-byte fields in the device and
+configuration descriptors, but not other descriptors, are converted
+to host endianness by the kernel.  This information is also shown
+in text form by the /proc/bus/usb/devices file, described later.
 
 These files may also be used to write user-level drivers for the USB
 devices.  You would open the /proc/bus/usb/BBB/DDD file read/write,

diff --git a/include/linux/usb/ch9.h b/include/linux/usb/ch9.h
index 73a2f4e..9b42bae 100644 (file)
--- a/include/linux/usb/ch9.h
+++ b/include/linux/usb/ch9.h
@@ -158,8 +158,12 @@ struct usb_ctrlrequest {
  * (rarely) accepted by SET_DESCRIPTOR.
  *
  * Note that all multi-byte values here are encoded in little endian
- * byte order "on the wire".  But when exposed through Linux-USB APIs,
- * they've been converted to cpu byte order.
+ * byte order "on the wire".  Within the kernel and when exposed
+ * through the Linux-USB APIs, they are not converted to cpu byte
+ * order; it is the responsibility of the client code to do this.
+ * The single exception is when device and configuration descriptors (but
+ * not other descriptors) are read from usbfs (i.e. /proc/bus/usb/BBB/DDD);
+ * in this case the fields are converted to host endianness by the kernel.
  */
 
 /*