Public bug reported:
Found this whilst developing a custom STM32 USB composite device using
CDCs. The custom USB device is based on the github TinyUSB stack.
Test Platform --> Ubuntu 25.10 6.17.0-6-generic using cutecom 0.60.0-RC1 serial
terminal app.
The USB device appears as /dev/ttyACMn (where n = 1 .. 4).
In cutecom, the serial device is configured to open with baudrate 115200.
dmesg trace below was generated via dynamic debugging +p enabled for
module cdc_acm.
Doing the following sequence of operations causes the kernel cdc_acm
module to generate an inconsistent sequence of TinyUSB (cdc_device.c)
CDC_REQUEST_SET_LINE_CODING actions.
Using cutecom....
Open the device.
Close the device.
Open the device again.
On the 2nd open I would expect to see the same list of events as per the 1st
open. Instead there is a rogue
acm_tty_set_termios of baudrate 4000000.
The fact this is coming from the cdc_acm driver rules out the cause being
cutecom or my TinyUSB device.
It is 100% repeatable.
In cutecom, Open the device...
[ 3881.071694] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x22, val 0x3, len 0x0,
result 0
[ 3881.071852] cdc_acm 2-4.1.1.2:1.2: acm_tty_set_termios - set line: 115200 0
0 8
[ 3881.076057] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x20, val 0x0, len 0x7,
result 7
[ 3881.080466] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x22, val 0x2, len 0x0,
result 0
[ 3881.084673] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x22, val 0x0, len 0x0,
result 0
In cutecom, Close the device...
[ 3890.506614] cdc_acm 2-4.1.1.2:1.2: acm_tty_set_termios - set line: 9600 0 0 8
[ 3890.506979] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x20, val 0x0, len 0x7,
result 7
[ 3890.511178] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x22, val 0x0, len 0x0,
result 0
[ 3890.513169] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_irq - urb shutting down with
status: -2
[ 3890.515198] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.517200] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.519198] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.521192] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.523190] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.525189] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.527218] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.529195] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.531196] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.533159] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.535198] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.537199] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.539193] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.541191] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.543204] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
[ 3890.545205] cdc_acm 2-4.1.1.2:1.3: acm_read_bulk_callback - urb shutting
down with status: -2
In cutecom, Open the device...
[ 3904.694254] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x22, val 0x3, len 0x0,
result 0
[ 3904.694281] cdc_acm 2-4.1.1.2:1.2: acm_tty_set_termios - set line: 115200 0
0 8
[ 3904.698579] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x20, val 0x0, len 0x7,
result 7
THIS NEXT LINE IS INCORRECT AND SHOULDN'T HAPPEN
[ 3904.698707] cdc_acm 2-4.1.1.2:1.2: acm_tty_set_termios - set line: 4000000 0
0 8
[ 3904.703036] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x20, val 0x0, len 0x7,
result 7
AND THIS ONE IS AN REPEAT OF THE ORIGINAL PROBABLY CAUSED DUE TO THE PRIMARY
ERROR BEFOREHAND.
[ 3904.703071] cdc_acm 2-4.1.1.2:1.2: acm_tty_set_termios - set line: 115200 0
0 8
[ 3904.707519] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x20, val 0x0, len 0x7,
result 7
[ 3904.711820] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x22, val 0x2, len 0x0,
result 0
[ 3904.715997] cdc_acm 2-4.1.1.2:1.2: acm_ctrl_msg - rq 0x22, val 0x0, len 0x0,
result 0
** Affects: ubuntu
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2136080
Title:
Ubuntu 25.10 CDC_REQUEST_SET_LINE_CODING sequence contains incorrect
baudrate
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