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USB: fix comment about endianness of descriptors

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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>
This commit is contained in:
Phil Endecott 2008-12-01 10:22:33 -05:00 committed by Greg Kroah-Hartman
parent c33ba39214
commit 9a9fafb894
2 changed files with 10 additions and 4 deletions
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6
Documentation/usb/proc_usb_info.txt
View file

@ -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,

8
include/linux/usb/ch9.h
View file

@ -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.
*/
/*