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
 
 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,
 
 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
  * (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.

  */
 
 /*
  */
 
 /*