[Bug 1958224] Re: brltty claiming cp210x devices on 22.04

Sun Oct 1 08:55:33 UTC 2023

Not sure what is fixed with 6.4-4ubuntu3.

I removed/purged brltty, rebooted (just to make sure) and checked the
/dev/ttyUSB0 availability:

[   89.311770] usb 3-3: new full-speed USB device number 4 using xhci_hcd
[   89.529433] usb 3-3: New USB device found, idVendor=1a86, idProduct=7523, bcdDevice= 2.64
[   89.529439] usb 3-3: New USB device strings: Mfr=0, Product=2, SerialNumber=0
[   89.529440] usb 3-3: Product: USB Serial
[   90.069647] usbcore: registered new interface driver usbserial_generic
[   90.069654] usbserial: USB Serial support registered for generic
[   90.074280] usbcore: registered new interface driver ch341
[   90.074290] usbserial: USB Serial support registered for ch341-uart
[   90.074300] ch341 3-3:1.0: ch341-uart converter detected
[   90.074810] usb 3-3: ch341-uart converter now attached to ttyUSB0
[   93.183733] usb 3-3: USB disconnect, device number 4
[   93.184054] ch341-uart ttyUSB0: ch341-uart converter now disconnected from ttyUSB0
[   93.184072] ch341 3-3:1.0: device disconnected

That works. After installing brltty and retrying, we see that /dev/ttyUSB0 is immediately stolen.

[  130.375473] usb 3-3: new full-speed USB device number 5 using xhci_hcd
[  130.593243] usb 3-3: New USB device found, idVendor=1a86, idProduct=7523, bcdDevice= 2.64
[  130.593249] usb 3-3: New USB device strings: Mfr=0, Product=2, SerialNumber=0
[  130.593250] usb 3-3: Product: USB Serial
[  130.595110] ch341 3-3:1.0: ch341-uart converter detected
[  130.595546] usb 3-3: ch341-uart converter now attached to ttyUSB0
[  131.168883] input: PC Speaker as /devices/platform/pcspkr/input/input17
[  131.677420] input: BRLTTY 6.4 Linux Screen Driver Keyboard as /devices/virtual/input/input18
[  131.797698] usb 3-3: usbfs: interface 0 claimed by ch341 while 'brltty' sets config #1
[  131.798107] ch341-uart ttyUSB0: ch341-uart converter now disconnected from ttyUSB0
[  131.798115] ch341 3-3:1.0: device disconnected

Here's the lsusb output:

# lsusb 
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 002: ID 27c6:609c Shenzhen Goodix Technology Co.,Ltd. Goodix USB2.0 MISC
Bus 003 Device 005: ID 1a86:7523 QinHeng Electronics CH340 serial converter
Bus 003 Device 003: ID 8087:0032 Intel Corp. AX210 Bluetooth
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Apparently, I'm not using a CP210x but a CH340. It suffers from the same problem though.

Having said that, I agree with Steve [~vorlon]:

> That represents a CRITICAL regression for the users in question.
> It effectively bricks their machine and requires the user to rely
> on a sighted person (who is also Ubuntu-knowledgeable) to get it
> working again.

We can just purge brltty and be done with it. So it's clearly the lesser
of two evils right now.

Walter

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https://bugs.launchpad.net/bugs/1958224

Title:
  brltty claiming cp210x devices on 22.04

Status in brltty package in Ubuntu:
  Fix Released
Status in brltty source package in Jammy:
  Fix Released
Status in brltty package in Debian:
  Confirmed

Bug description:
  * Impact

  The brltty udev rules are claiming generic devices IDs which makes
  some other devices like Arduino cards not able to interact with the
  serial port anymore

  * Test Case

  Try to use an Arduino over a cp210x or FTDI serial port, it should be
  able to talk to the computer

  - upgrades from focal/impish to the SRU version should have no
  question and no /etc/udev/rules.d/86-brltty-usbgeneric.rules generated

  - upgrades from brltty 6.4-4ubuntu2
  1. if a device matching the IDs 0403:6001 / 10C4:EA60 / 10C4:EA80 is connectect at the time of the upgrade it should prompt with the debconf question
  1.a if the answer is yes, /etc/udev/rules.d/86-brltty-usbgeneric.rules should be generated
  1.b if the answer is no, /etc/udev/rules.d/86-brltty-usbgeneric.rules not installed

  2. if no matching device is connected
  there should be no debconf question nor /etc/udev/rules.d/86-brltty-usbgeneric.rules generated

  - installing brltty when it was not installed
  no question and no config generated

  * Regression potential

  If the debconf logic is wrong users could be prompted with the
  question when not needed or not prompted when they should. If the udev
  rules was incorrect or wrongly installed it could lead to have brltty
  not starting when it should

  -------------------

  Distributor ID:	Ubuntu
  Description:	Ubuntu Jammy Jellyfish (development branch)
  Release:	22.04
  Codename:	jammy
  brltty:  Installed: 6.4-2ubuntu1

   brltty appears once again to be claiming cp210x devices with the
  vendor/product ID of:

  idVendor=10c4, idProduct=ea60

  Example dmesg output:
    999.215968] usb 3-6.3: New USB device found, idVendor=10c4, idProduct=ea60, bcdDevice= 1.00
  [  999.215973] usb 3-6.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
  [  999.215975] usb 3-6.3: Product: CP2103 USB to UART Bridge
  [  999.215977] usb 3-6.3: Manufacturer: Silicon Labs
  [  999.215978] usb 3-6.3: SerialNumber: 0005
  [  999.234070] usbcore: registered new interface driver usbserial_generic
  [  999.234081] usbserial: USB Serial support registered for generic
  [  999.235262] usbcore: registered new interface driver cp210x
  [  999.235272] usbserial: USB Serial support registered for cp210x
  [  999.235298] cp210x 3-6.3:1.0: cp210x converter detected
  [  999.237039] usb 3-6.3: cp210x converter now attached to ttyUSB0
  [  999.300049] input: PC Speaker as /devices/platform/pcspkr/input/input41
  [  999.807223] input: BRLTTY 6.4 Linux Screen Driver Keyboard as /devices/virtual/input/input42
  [  999.991926] usb 3-6.3: usbfs: interface 0 claimed by cp210x while 'brltty' sets config #1
  [  999.995045] cp210x ttyUSB0: cp210x converter now disconnected from ttyUSB0
  [  999.995066] cp210x 3-6.3:1.0: device disconnected

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