Re: USB network gadget / DWC3 issue

[Ferry Toth <fntoth@gmail.com>]

Hi

Op 30-03-2021 om 22:26 schreef Ferry Toth:
> Hi,
>
> Op 30-03-2021 om 18:17 schreef Felipe Balbi:
>> Hi,
>>
>> Andy Shevchenko <andy.shevchenko@gmail.com> writes:
>>> Hi!
>>>
>>> I have a platform with DWC3 in Dual Role mode. Currently I'm
>>> experimenting on v5.12-rc5 with a few patches (mostly configuration)
>>> applied [1]. I'm using Debian Unstable on the host machine and
>>> BuildRoot with the above mentioned kernel on the target.
>>>
>>> **So, scenario 0:
>>> 1. Run iperf3 -s on target
>>> 2. Run iperf3 -c ... -t 0 on the host
>>> 3.  0.00-10.36  sec   237 MBytes   192 Mbits/sec                  
>>> receiver
>>>
>>> **Scenario 1:
>>> 1. Now, detach USB cable, wait for several seconds, attach it back,
>>> repeat above:
>>> 0.00-9.94   sec   209 MBytes   176 Mbits/sec receiver
>>>
>>> Note the bandwidth drop (177 vs. 192).
>>>
>>> (Repeating scenario 1 will give now the same result)
>>>
>>> **Scenario 2.
>>> 1. Detach USB cable, attach a device, for example USB stick,
>>> 2. See it being enumerated and detach it.
>>> 3. Attach cable from host
>>> 4 .   0.00-19.36  sec   315 MBytes   136 Mbits/sec                  
>>> receiver
>>>
>>> Note even more bandwidth drop!
>>>
>>> (Repeating scenario 1 keeps the same lower bandwidth)
>>>
>>> NOTE, sometimes on this scenario after several seconds the target
>>> simply reboots (w/o any logs [from kernel] printed)!
>>>
>>> So, any pointers on how to debug and what can be a smoking gun here?
>>>
>>> Ferry reported this in [2]. There are different kernel versions and
>>> tools to establish the connection (like connman vs. none in my case).
>>>
>>> [1]: https://github.com/andy-shev/linux/
>>> [2]: https://github.com/andy-shev/linux/issues/31
>> dwc3 tracepoints should give some initial hints. Look at packets sizes
>> and period of transmission. From dwc3 side, I can't think of anything we
>> would do to throttle the transmission, but tracepoints should tell a
>> clearer story.
>>
> My testing (but yes, with difference kernel and network managed by 
> connman) shows:
>
> 1) on cold boot eem network gadget works fine
>
> 2) after unplug or warm reboot (which is also an unplug) it's broken, 
> speed is lost (|12.0 Mbits/sec from 200Mb/s normally)|, packets lost, 
> no configuration received from dhcp, occasional reboot, only way to 
> fix is cold boot
>
> 3) if before unplug `connmanctl disable gadget`, on replugging and 
> enabling it works fine
>
> My theory is that some HW register is disturbed on a surprise unplug, 
> but not reset on plug or warm boot. But on cold boot is cleared. Maybe 
> that can help to narrow down tracepoints?
>
I captured a plug after warm and after cold boot. This includes network 
setup (dhcp). You can find it in [2] or directly link here: 
https://github.com/andy-shev/linux/files/6232410/boot.zip