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SubjectRe: [PATCH v4] usb: gadget: u_ether: Replace netif_stop_queue with netif_device_detach
From
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
>>>
>>>
>

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