New: CH340 USB-serial converter wrong baud rate for 2400 and 1200 baud

https://bugzilla.kernel.org/show_bug.cgi?id=220225

            Bug ID: 220225
           Summary: CH340 USB-serial converter wrong baud rate for 2400
                    and 1200 baud
           Product: Drivers
           Version: 2.5
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: USB
          Assignee: [email protected]
          Reporter: [email protected]
        Regression: No

I have a USB-serial converter (AFAIR I bought it as a CH340G years ago), where setting the baud rate to 2400 or 1200 results in it sending at 380 baud instead. The problem is the same for Linux 6.12.27 and FreeBSD 14.2. But the USB-serial converter works for OpenBSD 7.6.

Linux dmesg when plugging it in:

[450228.160661] usb 3-2: new full-speed USB device number 27 using xhci_hcd
[450228.310942] usb 3-2: New USB device found, idVendor=1a86, idProduct=7523,
bcdDevice= 2.54
[450228.310957] usb 3-2: New USB device strings: Mfr=0, Product=2,
SerialNumber=0
[450228.310964] usb 3-2: Product: USB2.0-Ser!
[450228.316943] ch341 3-2:1.0: ch341-uart converter detected
[450228.329674] ch341-uart ttyUSB3: break control not supported, using
simulated break
[450228.329889] usb 3-2: ch341-uart converter now attached to ttyUSB3

lsusb -v output on GNU/Linux:

Bus 003 Device 027: ID 1a86:7523 QinHeng Electronics CH340 serial converter

root@notebook6:~# lsusb -s 3:27 -v

Bus 003 Device 027: ID 1a86:7523 QinHeng Electronics CH340 serial converter Negotiated speed: Full Speed (12Mbps)
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 255 Vendor Specific Class

  bDeviceSubClass         0 [unknown]
  bDeviceProtocol         0 
  bMaxPacketSize0         8
  idVendor           0x1a86 QinHeng Electronics
  idProduct          0x7523 CH340 serial converter
  bcdDevice            2.54
  iManufacturer           0 
  iProduct                2 USB2.0-Ser!
  iSerial                 0 
  bNumConfigurations      1

Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 0x0027
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 0
bmAttributes 0x80
(Bus Powered)
MaxPower 96mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 3
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 1 [unknown]
bInterfaceProtocol 2
iInterface 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x82 EP 2 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0020 1x 32 bytes
bInterval 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x02 EP 2 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0020 1x 32 bytes
bInterval 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0008 1x 8 bytes
bInterval 1
Device Status: 0x0000
(Bus Powered)

Corresponding FreeBSD bug report:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=287509

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