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authorPhil Endecott <usb_endian_patch@chezphil.org>2008-12-01 10:22:33 -0500
committerGreg Kroah-Hartman <gregkh@suse.de>2008-12-17 10:49:14 -0800
commit9a9fafb89433c5fd1331bac0c84c4b321e358b42 (patch)
tree918ec5c858d043304a47e8744cbee1ad96170298
parentc33ba392147a8506b1b43899fdea6069e27e4277 (diff)
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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>
-rw-r--r--Documentation/usb/proc_usb_info.txt6
-rw-r--r--include/linux/usb/ch9.h8
2 files changed, 10 insertions, 4 deletions
diff --git a/Documentation/usb/proc_usb_info.txt b/Documentation/usb/proc_usb_info.txt
index 077e9032d0c..fafcd472326 100644
--- 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 73a2f4eb1f7..9b42baed390 100644
--- 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.
*/
/*