Re: dwc3 gadget and USB3

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Thu, Mar 09, 2023, Joakim Tjernlund wrote:
> On Thu, 2023-03-09 at 19:56 +0000, Thinh Nguyen wrote:
> > On Thu, Mar 09, 2023, Joakim Tjernlund wrote:
> > > 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? 
> > > > 
> > 
> > There's no option in gadget configfs to allow you to do that at the
> > moment. You can disable LPM in dwc3 controller in the devicetree with
> > "snps,dis_enblslpm_quirk" instead.
> 
> Yes, I found that. Thanks.

Also note that LPM is for device operating in usb2 speed. If it's usb3
speeds, then you need to disable U3 suspend.

> 
> > 
> > If the host puts the gadget in suspend, the gadget won't be able to
> > communicate with the host until the host wakes the gadget up and starts
> > talking to the gadget again. The gadget may be able to signal the host
> > to wakeup via remote wakeup. Did you check if the device is in suspend?
> > If it's in suspend, is the gadget enabled with remote wakeup? Did the
> > NCM driver sent a remote wakeup signal to the host? I didn't verify, but
> > I suspect the NCM gadget driver isn't configured/implemented with remote
> > wakeup.
> 
> Then maybe NCM/RNDIS should inform/disable LPM in the device driver?
> One cannot have half an impl. of this feature.

Most drivers don't fully support every feature. They are implemented as
needed. I'm not familiar with NCM/RNDIS driver. Perhaps you can ping its
maintainer to see its current status to see if it needs to be updated.
Unless there's a quirk from the host/device, we shouldn't have to
disable LPM.

BR,
Thinh