diff options
| author | Phil Endecott <usb_endian_patch@chezphil.org> | 2008-12-01 10:22:33 -0500 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2008-12-17 10:49:14 -0800 |
| commit | 9a9fafb89433c5fd1331bac0c84c4b321e358b42 (patch) | |
| tree | 918ec5c858d043304a47e8744cbee1ad96170298 | |
| parent | c33ba392147a8506b1b43899fdea6069e27e4277 (diff) | |
| download | lwn-9a9fafb89433c5fd1331bac0c84c4b321e358b42.tar.gz lwn-9a9fafb89433c5fd1331bac0c84c4b321e358b42.zip | |
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.txt | 6 | ||||
| -rw-r--r-- | 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 077e9032d0cd..fafcd4723260 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 73a2f4eb1f7a..9b42baed3900 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. */ /* |