From 9a9fafb89433c5fd1331bac0c84c4b321e358b42 Mon Sep 17 00:00:00 2001 From: Phil Endecott Date: Mon, 1 Dec 2008 10:22:33 -0500 Subject: [PATCH] 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 Signed-off-by: Alan Stern Signed-off-by: Greg Kroah-Hartman --- Documentation/usb/proc_usb_info.txt | 6 ++++-- include/linux/usb/ch9.h | 8 ++++++-- 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. */ /* -- 2.20.1