ubuntu 18.04 and missing ttyS4 (dw-apb-uart.8)

b0b0tiken

Hello!

I am using the latest Ubuntu 18.04 with the up squared.

I bought the cable with the 2 usb 2.0 and uart and connected it.

I cannot get /dev/ttyS4 to show up no matter what (nor /dev/ttyS5).

Kernel: 4.15.0-22-generic

During boot, I see /dev/ttyS4 and /dev/ttyS5.

$ dmesg | grep 16550
[ 2.460429] Serial: 8250/16550 driver, 32 ports, IRQ sharing enabled
[ 10.252343] dw-apb-uart.8: ttyS4 at MMIO 0x91524000 (irq = 4, base_baud = 115200) is a 16550A
[ 10.272381] dw-apb-uart.9: ttyS5 at MMIO 0x91522000 (irq = 5, base_baud = 115200) is a 16550A

$ dmesg | grep tty
[ 0.000000] console [tty0] enabled
[ 10.252343] dw-apb-uart.8: ttyS4 at MMIO 0x91524000 (irq = 4, base_baud = 115200) is a 16550A
[ 10.252515] serial serial0: tty port ttyS4 registered
[ 10.272381] dw-apb-uart.9: ttyS5 at MMIO 0x91522000 (irq = 5, base_baud = 115200) is a 16550A
[ 10.272549] serial serial1: tty port ttyS5 registered

$ sudo cat /proc/tty/driver/serial
serinfo:1.0 driver revision:
0: uart:unknown port:000003F8 irq:4
1: uart:unknown port:000002F8 irq:3
2: uart:unknown port:000003E8 irq:4
3: uart:unknown port:000002E8 irq:3
4: uart:16550A mmio:0x91524000 irq:4 tx:0 rx:0
5: uart:16550A mmio:0x91522000 irq:5 tx:0 rx:0

I even tried creating the node:
$ sudo mknod /dev/ttyS4 c 4 68

and tried to configure it:
sudo setserial /dev/ttyS4 uart 16550A
/dev/ttyS4: No such device or address

Has anyone any ideas I could try ?

Cheers,

b0b0

ccalde

Hi @b0b0tiken,

You should typically be using /dev/ttyS0 to access the UART on the 10-pin USB+UART connector.
However, it looks like this device entry might not be appearing with that kernel. And,
of course, we don’t yet support this kernel as far as I know.

It’s a generic kernel anyway, so you should probably raise this with the Ubuntu
kernel maintainers instead via Launchpad.

https://wiki.up-community.org/Software
https://wiki.up-community.org/Ubuntu

Cheers!

hhuysqt

Hi, I also have this issue, and I found that it is the serdev driver that vanishes the /dev/ttySx, because it wants to move the serial bus drivers from user space to kernel space, such as bluetooth and so on.
But yet RTL8723BS doesn't have bluetooth support, so you may need some kernel patches. These patches added rtl8723bs support in drivers/bluetooth, while this patch simply creates an exception for 8723 in drivers/acpi so that the old systemd bluetooth driver could be used.

ccalde

Hi @hhuysqt ,

Are you using the Ubuntu 18 as well?

We must be sure this issue is not present using the UP Ubuntu software.

Cheers!