PROBLEM: Sun Ultra 60 hangs on boot since Linux 6.8

[Nick Bowler]

Hi,

Linux 6.8 (and 6.8.1) are hanging on boot on my Ultra 60, right after
mounting the root filesystem.  This is a regression from 6.7, which
boots without any such problem.

Everything looks pretty normal, up to:

  [...]
  Run /sbin/init as init process
  INIT:

and the abnormal behaviour is that the boot appears to be stuck at
this point with no further output on the console.

I bisected to this commit:

  commit 45a3a8ef81291b63a2b50a1a145857dd9fc05e89
  Author: Tony Lindgren <tony@xxxxxxxxxxx>
  Date:   Mon Nov 13 10:07:53 2023 +0200
  
      serial: core: Revert checks for tx runtime PM state

Reverting this commit on top of Linux 6.8 is sufficient to get the
system booting again.

The console output related to the serial port (or anything else) does
not appear to be any different on a failing versus working kernel:

  f0061e88: ttyS0 at MMIO 0x1fff1400000 (irq = 7, base_baud = 115200) is a SAB82532 V3.2
  Console: ttyS0 (SAB82532)
  printk: legacy console [ttyS0] enabled
  f0061e88: ttyS1 at MMIO 0x1fff1400040 (irq = 7, base_baud = 115200) is a SAB82532 V3.2
  Serial: 8250/16550 driver, 1 ports, IRQ sharing disabled
  serial 0000:00:05.0: enabling device (0000 -> 0001)
  0000:00:05.0: ttyS2 at I/O 0x1fe02010c00 (irq = 17, base_baud = 115200) is a 16550A

In case it helps, I attached the complete console output from a failing
boot (gzipped).

Let me know if you need any more info!

Thanks,
  Nick

Attachment: console-boot.log.gz
Description: application/gzip