Re: hiddev

> > > HIDIOCGSTRING - struct hiddev_string_descriptor (read/write) Gets a 
> > > string descriptor from the device. The caller must fill in the "index" 
> > > field to indicate which descriptor should be returned.
> > Can you please tell me in what range this index is?
> 
> Please refer to USB specification.
> The string descriptor indexes are fully optional and are referenced by the 
> other descriptors (device descriptors, configuration descriptors, etc). So 
> the valid range differs from device to device and depends of how much of 
> the descriptor information has available the corresponding string (human 
> readable) representation.

Yes I understood that. I needed this info to investigate an USB device
for which no documentation exists. But I think I found the information
that I need:
in linux/drivers/usb/core/message.c there's the following code snippet:
                result = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
                        USB_REQ_GET_DESCRIPTOR, USB_DIR_IN,
                        (USB_DT_STRING << 8) + index, langid, buf, size,
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
That means that index may not be bigger then 255 as else it would garble the
value of 'USB_DT_STRING << 8'.


Folkert van Heusden

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