fix super-speed handling

[js731ca]

from one of our contractors:

umtp-responder: fix super-speed handling
     
     Add the patches required to configure the USB SuperSpeed descriptors
     correctly. Without the patches the host USB SuperSpeed negotiation fails
     and the USB OTG mechanism (autom. host<->device switch) fails too.
     
     Signed-off-by: Marco Felsch <[email protected]>

---

Albeit the name suggesting it, this option is not used for
the USB descriptor setup instead it is only the MTP protocol which uses it.

An usage example on i.MX8MP - which supports USB2.0 OTG and USB3.0 OTG:

## /etc/umtprd/umtprd.conf

# SuperSpeed max. package size is 1024
usb_max_packet_size 0x400

[jfdelnero]

Hello,

@js731ca i am trying to remove this last "usb_max_packet_size" user defined variable.

But for this i need to find a way to know which packet size i need to use when the connection is established.

To do this i need to know one of these points :

• Which speed is used ?

or

• Which descriptor is finally used for the current connection.

or even better :

• What is the current wMaxPacketSize used.

Have you any idea how to get on of these information through the GadgetFS / FunctionFS layer ?

[js731ca]

@bith3ad these patches came initially from you, wanna chime in? :-)
in the commits it's mentioned that the values are according to the USB-specification.
my first guess would be to look at the sysfs entries of the udc (usb device controller) the usb-gadget uses?