[v4,2/2] usb/gadget: Add driver for Aspeed SoC virtual hub

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Sat, 2018-03-17 at 09:50 -0400, Alan Stern wrote:
> On Sat, 17 Mar 2018, Benjamin Herrenschmidt wrote:
> 
> > On Fri, 2018-03-16 at 16:56 -0400, Alan Stern wrote:
> > > On Fri, 16 Mar 2018, Benjamin Herrenschmidt wrote:
> > > 
> > > > On Thu, 2018-03-15 at 08:03 +1100, Benjamin Herrenschmidt wrote:
> > > > > > > Do you have more comments for the rest of the driver or that's it ?
> > > > > > 
> > > > > > so far, that's it.
> > > > > 
> > > > > Ok. I'll re-send.
> > > > 
> > > > So I'll resend in a minute, doing a few more tests, however, I've
> > > > noticed something which I wont' have time to track down til at
> > > > best next week, I wonder if it's normal/expected.
> > > > 
> > > > If I just create a mass storage function set to be "removable" and
> > > > "cdrom" with no file attached,  and enable it, I get an endless stream
> > > > of resets. It looks like the host constantly does USB resets.
> > > 
> > > That's not why I get.  There's an endless stream of messages, but it
> > > doesn't include any resets.  Just command failures and endpoint halts.  
> > > For example:
> > 
> >  .../...
> > 
> > In my case, I was getting resets on the host:
> 
 .../...

> Output from usbmon could help.

So that ended up being a bug in my UDC driver. For IN requests I had a
problem with 0-length requests when enabling the multi-descriptor mode
in the EP which seems to affect some MODE_SENSE responses among others.

I fixed that and now see only the silent errors you mentioned.

Felipe, I'll send a respin of the driver with a fix tomorrow.

 .../...

> Maybe...  Even after cdrom support was added to the gadget, the scope 
> was limited.  It was intended to emulate _only_ a CD drive, not a DVD 
> drive.
> 
> Also, if I'm not mistaken, the commands that the emulation doesn't 
> handle are all optional.

Right. One low hanging fruit seems to be 
GET_EVENT_STATUS_NOTIFICATION (0x4a). I'll look into it in my copious
spare time ;-)

There are a few more, which as long as we only support "read only"
CD/DVD should be fairly easy to deal with.

Cheers,
Ben.

> Alan Stern
> 
> > The Aspeed chip is a BMC chip, ie server management processor, and is
> > connected via the USB gadget to the actual server (the host). One of
> > the usage scenario here is to use USB gadget to present distro ISOs as
> > USB CD/DVDs to the host for remote provisioning (sourced over the
> > network via something like nbd).
> > 
> > Note that due to the limitation of having to use a file or a block
> > device, we might end up doing a userspace CDROM emulation instead that
> > can source ISOs via things like HTTPS instead, but initially the above
> > is what we are toying with.
> > 
> > Cheers,
> > Ben.
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