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Date: Sun, 28 Apr 2024 23:07:36 +0200
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Subject: Re: [PATCH v4] usb: gadget: u_ether: Replace netif_stop_queue with
 netif_device_detach
From: Ferry Toth <fntoth@gmail.com>
To: Hardik Gajjar <hgajjar@de.adit-jv.com>,
 Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: gregkh@linuxfoundation.org, s.hauer@pengutronix.de, jonathanh@nvidia.com,
 linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
 quic_linyyuan@quicinc.com, paul@crapouillou.net, quic_eserrao@quicinc.com,
 erosca@de.adit-jv.com
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Hi,

Op 25-04-2024 om 23:27 schreef Ferry Toth:
> 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();

I tried to get a more useful trace:
root@yuna:/sys/kernel/tracing# echo 'gether_*' > set_ftrace_filter
root@yuna:/sys/kernel/tracing# echo 'eem_*' >> set_ftrace_filter
root@yuna:/sys/kernel/tracing# echo function > current_tracer
root@yuna:/sys/kernel/tracing# echo 'reset_config' >> set_ftrace_filter
-> switch to host mode then back to device
root@yuna:/sys/kernel/tracing# cat trace
# tracer: function
#
# entries-in-buffer/entries-written: 53/53   #P:2
#
#                                _-----=> irqs-off/BH-disabled
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| / _-=> migrate-disable
#                              |||| /     delay
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
      irq/68-dwc3-523     [000] D..3.   133.990254: reset_config 
<-__composite_disconnect
      irq/68-dwc3-523     [000] D..3.   133.992274: eem_disable 
<-reset_config
      irq/68-dwc3-523     [000] D..3.   133.992276: gether_disconnect 
<-reset_config
      kworker/1:3-443     [001] ...1.   134.022453: eem_unbind 
<-purge_configs_funcs

-> to device mode

      kworker/1:3-443     [001] ...1.   148.630773: eem_bind 
<-usb_add_function
      irq/68-dwc3-734     [000] D..3.   149.155209: eem_set_alt 
<-composite_setup
      irq/68-dwc3-734     [000] D..3.   149.155215: gether_disconnect 
<-eem_set_alt
      irq/68-dwc3-734     [000] D..3.   149.155220: gether_connect 
<-eem_set_alt
      irq/68-dwc3-734     [000] D..3.   149.157287: eem_set_alt 
<-composite_setup
      irq/68-dwc3-734     [000] D..3.   149.157292: gether_disconnect 
<-eem_set_alt
      irq/68-dwc3-734     [000] D..3.   149.159338: gether_connect 
<-eem_set_alt
      irq/68-dwc3-734     [000] D..2.   149.239625: eem_unwrap <-rx_complete
..

I don't know where to look exactly. Any hints?

> 
>> 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 don't know what you mean here. Which driver do you mean?

>>>
>>>>>> 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
>>>
>>>
>