Re: Pass transfer_buffer to gadget drivers

[Felipe Balbi <felipe.balbi@linux.intel.com>]

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Hi,

Andrey Konovalov <andreyknvl@google.com> writes:
> I've noticed that when the host performs a control request,
> urb->transfer_buffer/transfer_buffer_length are not passed to the
> gadget drivers via the setup() call, the only thing that is passed is
> the usb_ctrlrequest struct. Is there a way to get the transfer_buffer
> from within a gadget driver? If not, what approach would the best to
> implement this?

I think you need to further explain what you mean here.

What do you mean by gadget driver in this case?

If you mean the drivers under drivers/usb/gadget/{function,legacy}
directories then there's no way that they can have access to anything
from the host.

Remember that gadget and host are two completely distinct units. The
only thing they share is a USB cable. When it comes to Control
Transfers, if a data stage is necessary, that must be encoded in the
wLength field of the control structure.

Also, host side does *not* pass its usb_ctrlrequest struct to the
gadget, it passes a series of 8 bytes which are oblivious to where in
memory they were from the host point of view.

If if you have the same machine acting as both host and device, each
side has no knowledge of that fact.

-- 
balbi

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