Re: Testing endpoint halt support for raw-gadget

[Andrey Konovalov <andreyknvl@google.com>]

On Mon, Apr 27, 2020 at 9:51 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> 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.

Or maybe somehow expose all endpoints and their features (like
GadgetFS) and let userspace put proper addresses into endpoint
descriptors before enumeration starts.