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SubjectRe: [PATCH v4] usb: gadget: u_ether: Replace netif_stop_queue with netif_device_detach
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Hi,

Op 17-04-2024 om 17:13 schreef Hardik Gajjar:
> On Tue, Apr 16, 2024 at 04:48:32PM +0300, Andy Shevchenko wrote:
>> On Thu, Apr 11, 2024 at 10:52:36PM +0200, Ferry Toth wrote:
>>> Op 11-04-2024 om 18:39 schreef Andy Shevchenko:
>>>> On Thu, Apr 11, 2024 at 04:26:37PM +0200, Hardik Gajjar wrote:
>>>>> On Wed, Apr 10, 2024 at 08:37:42PM +0300, Andy Shevchenko wrote:
>>>>>> On Sun, Apr 07, 2024 at 10:51:51PM +0200, Ferry Toth wrote:
>>>>>>> Op 05-04-2024 om 13:38 schreef Hardik Gajjar:
>>
>> ...
>>
>>>>>>> Exactly. And this didn't happen before the 2 patches.
>>>>>>>
>>>>>>> To be precise: /sys/class/net/usb0 is not removed and it is a link, the link
>>>>>>> target /sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/net/usb0 no
>>>>>>> longer exists
>>>>> So, it means that the /sys/class/net/usb0 is present, but the symlink is
>>>>> broken. In that case, the dwc3 driver should recreate the device, and the
>>>>> symlink should become active again
>>>
>>> Yes, on first enabling gadget (when device mode is activated):
>>>
>>> root@yuna:~# ls /sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/
>>> driver  net  power  sound  subsystem  suspended  uevent
>>>
>>> Then switching to host mode:
>>>
>>> root@yuna:~# ls /sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/
>>> ls: cannot access
>>> '/sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/': No such file
>>> or directory
>>>
>>> Then back to device mode:
>>>
>>> root@yuna:~# ls /sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/
>>> driver  power  sound  subsystem  suspended  uevent
>>>
>>> net is missing. But, network functions:
>>>
>>> root@yuna:~# ping 10.42.0.1
>>> PING 10.42.0.1 (10.42.0.1): 56 data bytes
>>>
>>> Mass storage device is created and removed each time as expected.
>>
>> So, what's the conclusion? Shall we move towards revert of those two changes?
>
>
> As promised, I have the tested the this patch with the dwc3 gadget. I could not reproduce
> the issue.
>
> I can see the usb0 exist all the time and accessible regardless of the role switching of the USB mode (peripheral <-> host)
>
> Following are the logs:
> //Host to device
>
> console:/sys/bus/platform/devices/a800000.ssusb # echo "peripheral" > mode
> console:/sys/bus/platform/devices/a800000.ssusb # ls a800000.dwc3/gadget/net/
> usb0
>
> //device to host
> console:/sys/bus/platform/devices/a800000.ssusb # echo "host" > mode
> console:/sys/bus/platform/devices/a800000.ssusb # ls a800000.dwc3/gadget/net/
> usb0

That is weird. When I switch to host mode (using the physical switch),
the whole gadget directory is removed (now testing 6.9.0-rc5)

Switching back to device mode, that gadget directory is recreated. And
gadget/sound as well, but not gadget/net.

> s a800000.dwc3/gadget/net/usb0 <
> addr_assign_type duplex phys_port_name
> addr_len flags phys_switch_id
> address gro_flush_timeout power
> broadcast ifalias proto_down
> carrier ifindex queues
> carrier_changes iflink speed
> carrier_down_count link_mode statistics
> carrier_up_count mtu subsystem
> dev_id name_assign_type tx_queue_len
> dev_port netdev_group type
> device operstate uevent
> dormant phys_port_id waiting_for_supplier
> console:/sys/bus/platform/devices/a800000.ssusb # ifconfig -a usb0
> usb0 Link encap:Ethernet HWaddr 3a:8b:63:97:1a:9a
> BROADCAST MULTICAST MTU:1500 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:1000
> RX bytes:0 TX bytes:0
>
> console:/sys/bus/platform/devices/a800000.ssusb #
>
> I strongly advise against reverting the patch solely based on the observed issue of removing the /sys/class/net/usb0 directory while the usb0 interface remains available.

There's more to it. I also mentioned that switching the role or
unplugging the cable leaves the usb0 connection.

I have while in host mode:
root@yuna:~# ifconfig -a usb0
usb0: flags=-28605<UP,BROADCAST,RUNNING,MULTICAST,DYNAMIC> mtu 1500
inet 10.42.0.221 netmask 255.255.255.0 broadcast 10.42.0.255
inet6 fe80::a8bb:ccff:fedd:eef1 prefixlen 64 scopeid 0x20<link>


You don't see that because you didn't create a connection at all.

> Instead, I recommend enabling FTRACE to trace the functions involved and identify which faulty call is responsible for removing usb0.

Switching from device -> host -> device:

root@yuna:~# trace-cmd record -p function_graph -l *gether_*
plugin 'function_graph'
Hit Ctrl^C to stop recording
^CCPU0 data recorded at offset=0x1c8000
188 bytes in size (4096 uncompressed)
CPU1 data recorded at offset=0x1c9000
0 bytes in size (0 uncompressed)
root@yuna:~# trace-cmd report
cpus=2
irq/68-dwc3-725 [000] 514.575337: funcgraph_entry: #
2079.480 us | gether_disconnect();
irq/68-dwc3-946 [000] 524.263731: funcgraph_entry: +
11.640 us | gether_disconnect();
irq/68-dwc3-946 [000] 524.263743: funcgraph_entry: !
116.520 us | gether_connect();
irq/68-dwc3-946 [000] 524.268029: funcgraph_entry: #
2057.260 us | gether_disconnect();
irq/68-dwc3-946 [000] 524.270089: funcgraph_entry: !
109.000 us | gether_connect();


> According to current kernel architecture of u_ether driver, only gether_cleanup should remove the usb0 interface along with its kobject and sysfs interface.
> I suggest sharing the analysis here to understand why this practice is not followed in your use case or driver ?

Yes, I'll try to trace where that happens.

Nevertheless, the disappearance of the net/usb0 directory seems
harmless? But the usb: net device remaining after disconnect or role
switch is not good, as the route remains.

May be they are 2 separate problems. Could you try to reproduce what
happens if you make eem connection and then unplug?

> I am curious why the driver was developed without adhering to the kernel's gadget architecture.
>
>>
>>>>> I have the dwc3 IP base usb controller, Let me check with this patch and
>>>>> share result here. May be we need some fix in dwc3
>>> Would have been nice if someone could test on other controller as well. But
>>> another instance of dwc3 is also very welcome.
>>>> It's quite possible, please test on your side.
>>>> We are happy to test any fixes if you come up with.
>>
>> --
>> With Best Regards,
>> Andy Shevchenko
>>
>>


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