Hi,

I sometimes need more than the built in serial port so I bought a PCI
4-port serial card.

The kernel apparently recognizes the card.

lspci output:
04:00.0 Serial controller: MosChip Semiconductor Technology Ltd. 4-Port
PCIe Serial Adapter
04:00.1 Serial controller: MosChip Semiconductor Technology Ltd. 4-Port
PCIe Serial Adapter
04:00.2 Serial controller: MosChip Semiconductor Technology Ltd. 4-Port
PCIe Serial Adapter
04:00.3 Serial controller: MosChip Semiconductor Technology Ltd. 4-Port
PCIe Serial Adapter

The motherboard serial port shows up at /dev/ttyS0.

Three of the PCI card's ports get assigned and work ok:

ls -l /dev/ttyS*
crw-rw---- 1 root dialout 4, 64 Apr 15 09:50 /dev/ttyS0
crw-rw---- 1 root dialout 4, 65 Apr 1 08:32 /dev/ttyS1
crw-rw---- 1 root dialout 4, 66 Apr 1 08:26 /dev/ttyS2
crw-rw---- 1 root dialout 4, 67 Apr 1 08:28 /dev/ttyS3

However, the fourth PCI port doesn't get assigned.

/var/log/dmesg
[    0.285396] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
[    0.285713] 00:04: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) 
is a 16550A
[    0.286999] 0000:04:00.0: ttyS1 at I/O 0xd030 (irq = 19, base_baud = 
115200) is a 16550A
[    0.288048] 0000:04:00.1: ttyS2 at I/O 0xd020 (irq = 16, base_baud = 
115200) is a 16550A
[    0.288481] 0000:04:00.2: ttyS3 at I/O 0xd010 (irq = 17, base_baud = 
115200) is a 16550A
[    0.288596] serial 0000:04:00.3: Couldn't register serial port d000, 
irq 18, type 0, error -28

I haven't been able to find out what error code -28 is other than out of
space.

How can the fourth port be assigned as: /dev/ttyS4?

Best regards,
Fred
(subscribed)