Re: dwc3 gadget and USB3

[Joakim Tjernlund <Joakim.Tjernlund@infinera.com>]

On Thu, 2023-03-09 at 17:32 +0100, Joakim Tjernlund wrote:
> On Wed, 2023-03-08 at 22:26 +0100, Joakim Tjernlund wrote:
> > On Wed, 2023-03-08 at 19:58 +0100, gregkh@linuxfoundation.org wrote:
> > > On Wed, Mar 08, 2023 at 06:12:51PM +0000, Joakim Tjernlund wrote:
> > > > On Wed, 2023-03-08 at 18:25 +0100, Greg KH wrote:
> > > > > On Wed, Mar 08, 2023 at 05:10:17PM +0000, Joakim Tjernlund wrote:
> > > > > > we are using fsl-ls1043a-rdb based design but with a ls1023a SOC and
> > > > > > use USB0 in gadget mode running either NCM or RNDIS ethernet on top.
> > > > > > 
> > > > > > When we connect the gadget to a PC(Linux of Windows) over an USB2 hub,
> > > > > > networking(NCM or RNDIS) works well.
> > > > > > 
> > > > > > However, when we connect the gadget directly to the PC/laptop which uses USB3
> > > > > > we see something odd:
> > > > > >   Ping from PC to gadget works.
> > > > > >   Ping from gadget to laptop does not. However if we also ping from PC at the same time we
> > > > > >   see gadget to PC start working.
> > > > > > Seems like ping from the PC tiggers the gadget to see incoming pkgs somehow.
> > > > > > 
> > > > > > Any idea what might be wrong or how to debug this?
> > > > > > Kernel 5.15.87
> > > > > 
> > > > > 5.15.y is very old, does this also happen on 6.2?
> > > > > 
> > > > 
> > > > I just tried 6.1.15 and the problem remains, I hope that is close enough ?
> > > 
> > > It's good enough :)
> > > 
> > > Have any logs at all that show any problems?
> > > 
> > No, don't know where to start. There are no errors logged.
> > 
> > >   Also, you might want to
> > >  cc:  the dwc3 maintainer...
> > 
> > I thought I did but that look like old info, added Thinh Nguyen now, thanks
> > 
> >  Jocke
> > 
> > > 
> > >  thanks,
> > > 
> > >  greg k-hj
> > 
> 
> Found and USBC Dock and connected that between gadget an PC and this also works well.
> Seems like a hub, regardless of USB2/USB3, make the usb network function in both directions.
> 
> Found out something interesting, on PC:
> cd /sys/devices/pci0000:00/0000:00:14.0/usb1/1-1/power  # Where my gadget is connected
> echo 0 > usb2_hardware_lpm
> 
> Now ping works normally.
> 
> So LPM does not seem to work properly on gadget. Can I disable LPM somehow
> on gadget side? 
> 
>  Jocke

Found some DTS quirks to disable LPM, work fine :)
One observation:

ping over NCM to Linux PC:
PING 169.254.100.102 (169.254.100.102): 56 data bytes
64 bytes from 169.254.100.102: seq=0 ttl=64 time=2.166 ms
64 bytes from 169.254.100.102: seq=1 ttl=64 time=2.168 ms
64 bytes from 169.254.100.102: seq=2 ttl=64 time=2.333 ms

ping over NCM to Windows 10 PC:
PING 169.254.100.102 (169.254.100.102): 56 data bytes
64 bytes from 169.254.100.102: seq=0 ttl=128 time=0.921 ms
64 bytes from 169.254.100.102: seq=1 ttl=128 time=0.963 ms
64 bytes from 169.254.100.102: seq=2 ttl=128 time=1.143 ms
64 bytes from 169.254.100.102: seq=3 ttl=128 time=1.161 ms

NCM to Windows appears to have much lower latency.

 Jocke