Description of problem:

Customer has a machine with the Synopsys DesignWare APB UART. The serial ports
are MMIO based:

[ 4.587543] dw-apb-uart.6: ttyS0 at MMIO 0x4017006000 (irq = 33, base_baud = 6250000) is a 16550A
[ 4.599879] dw-apb-uart.7: ttyS1 at MMIO 0x4017007000 (irq = 16, base_baud = 6250000) is a 16550A

Kernel is configured to use ttyS0 as console:

BOOT_IMAGE=(hd1,gpt2)/vmlinuz-5.14.0-162.6.1.el9_1.x86_64 root=/dev/mapper/rhel-root ro rhgb quiet crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap console=ttyS0,115200n8

So on system boot, a serial-getty@ttyS0 should be be started automatically by
systemd-getty-generator but it fails to do it.

Version-Release number of selected component (if applicable):

RHEL 9.1

How reproducible:

Always

Steps to Reproduce:
1. Install RHEL 9.1 on a machine whose serial ports are MMIO-based.
2. Reboot the system
3. Check if a serial-getty@ttyS0 is started

Actual results:

serial-getty@ttyS0 is not started

Expected results:

serial-getty@ttyS0 should be started

Additional info:

From the system sosreport:

$ fgrep w -e ttyS0 -e getty sos_commands/logs/journalctl_no-pager_catalog_-boot
Mar 08 09:17:25 localhost kernel: Command line: BOOT_IMAGE=(hd1,gpt2)/vmlinuz-5.14.0-162.6.1.el9_1.x86_64 root=/dev/mapper/rhel-root ro rhgb quiet crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap console=ttyS0,115200n8
Mar 08 09:17:25 localhost kernel: Kernel command line: BOOT_IMAGE=(hd1,gpt2)/vmlinuz-5.14.0-162.6.1.el9_1.x86_64 root=/dev/mapper/rhel-root ro rhgb quiet crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap console=ttyS0,115200n8
Mar 08 09:17:25 localhost kernel: printk: console [ttyS0] enabled
Mar 08 09:17:25 localhost dracut-cmdline[353]: Using kernel command line parameters: BOOT_IMAGE=(hd1,gpt2)/vmlinuz-5.14.0-162.6.1.el9_1.x86_64 root=/dev/mapper/rhel-root ro rhgb quiet crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap console=ttyS0,115200n8
Mar 08 09:17:27 localhost systemd[1]: Created slice Slice /system/getty.
Mar 08 09:17:28 localhost kernel: printk: console [ttyS0] disabled
Mar 08 09:17:28 localhost kernel: dw-apb-uart.6: ttyS0 at MMIO 0x4017006000 (irq = 33, base_baud = 6250000) is a 16550A
Mar 08 09:17:28 localhost kernel: printk: console [ttyS0] enabled
– Subject: A start job for unit getty@tty1.service has finished successfully
– A start job for unit getty@tty1.service has finished successfully.
– Subject: A start job for unit getty.target has finished successfully
– A start job for unit getty.target has finished successfully.

As can be seen, ttyS0 is enabled too late. Because of this, the getty service
generator (systemd-getty-generator) does not create getty@ttyS0.service. I have
seen a similar problem on RHEL 8 and filed a bug report for it:

MMIO-based serial port does not work during the installation but works later
https://bugzilla.redhat.com/show_bug.cgi?id=2162741

The behavior on RHEL 9 is better, since it is still possible to install the OS.

It's possible to circumvent the problem by enabling the service explicitly:

1. systemctl enable --now serial-getty@ttyS0.service