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Date: Thu, 25 Apr 2024 23:27:47 +0200
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Subject: Re: [PATCH v4] usb: gadget: u_ether: Replace netif_stop_queue with
 netif_device_detach
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
References: <20240115132720.GA98840@vmlxhi-118.adit-jv.com>
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 <321e908e-0d10-4e36-8dc4-6997c73fe2eb@gmail.com>
 <ZhbOZsp-XHemVhQz@smile.fi.intel.com>
 <20240411142637.GA110162@vmlxhi-118.adit-jv.com>
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 <20240417151342.GA56989@vmlxhi-118.adit-jv.com>
Content-Language: en-US
From: Ferry Toth <fntoth@gmail.com>
In-Reply-To: <20240417151342.GA56989@vmlxhi-118.adit-jv.com>
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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
>>
>>