Re: Testing endpoint halt support for raw-gadget

[Andrey Konovalov <andreyknvl@google.com>]

On Fri, Apr 24, 2020 at 9:36 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> On Fri, Apr 10, 2020 at 2:29 AM Alan Stern <stern@rowland.harvard.edu> wrote:
> >
> > On Thu, 9 Apr 2020, Andrey Konovalov wrote:
> >
> > > Hi Alan and Greg,
> > >
> > > I've been thinking about what kind of features raw-gadget might be
> > > missing, that would allow more flexibility in emulating USB devices.
> > > One of the things that is currently missing is halting endpoints.
> > > Adding this functionality seems to be fairly easy, but it's unclear to
> > > me how to test it. Any suggestions?
> >
> > You should use the usbtest driver along with the testusb program in
> > tools/usb.  Of course, to do it you will need a userspace driver for
> > raw-gadget.  usbtest works best with gadget-zero, but it can be used
> > (in degraded form) with any USB device.
>
> Hi Alan,
>
> I've started working on a test suite for raw-gadget based on the
> usbtest module as you suggested and have a few questions:

Another question, which actually seems to be a major problem.

It looks like automatic endpoint selection based on required features
doesn't work in raw-gadget. The way it tries to do that is iterating
over the list of available endpoints and finding one that has the
right direction and transfer type. But it seems that the right way to
do that (like it's done in usb_ep_autoconfig()) is to also patch the
bEndpointAddress field of the endpoint descriptor.

Currently with raw-gadget the endpoints are supposed to be enabled
after a set_configuration/set_interface request from the host, so it's
too late to patch the endpoint descriptor (the one that was sent to
the host during enumeration). I'm guessing that sending one endpoint
descriptor during enumeration and then using a different one (with
patched bEndpointAddress) to set ep->desc before doing usb_ep_enable()
won't work (as there's going to be mismatch in endpoint addresses
between the host and the UDC), right?

I wonder what we can do about that. It seems that we actually need to
parse the descriptors and figure out the right endpoints before the
enumeration starts.