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>
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@ -49,8 +49,10 @@ it and 002/048 sometime later.
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These files can be read as binary data. The binary data consists
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of first the device descriptor, then the descriptors for each
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configuration of the device. That information is also shown in
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text form by the /proc/bus/usb/devices file, described later.
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configuration of the device. Multi-byte fields in the device and
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configuration descriptors, but not other descriptors, are converted
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to host endianness by the kernel. This information is also shown
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in text form by the /proc/bus/usb/devices file, described later.
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These files may also be used to write user-level drivers for the USB
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devices. You would open the /proc/bus/usb/BBB/DDD file read/write,
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@ -158,8 +158,12 @@ struct usb_ctrlrequest {
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* (rarely) accepted by SET_DESCRIPTOR.
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*
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* Note that all multi-byte values here are encoded in little endian
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* byte order "on the wire". But when exposed through Linux-USB APIs,
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* they've been converted to cpu byte order.
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* byte order "on the wire". Within the kernel and when exposed
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* through the Linux-USB APIs, they are not converted to cpu byte
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* order; it is the responsibility of the client code to do this.
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* The single exception is when device and configuration descriptors (but
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* not other descriptors) are read from usbfs (i.e. /proc/bus/usb/BBB/DDD);
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* in this case the fields are converted to host endianness by the kernel.
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*/
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/*
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