PNP0501 serial driver takes almost 2 seconds to suspend/resume (printk issue)

Todd Brandt
2022-07-07T20:31:57Z

Ever since 5.19.0-rc1 the serial device has taken almost a second
longer in both suspend and resume. This effect is witnessed in half the
machines in our lab (~10 machines). It occurs on dell, asus, gigabyte
and other machines so it's not hardware specific.

I opened a bugzilla issue which includes the git bisect:
https://bugzilla.kernel.org/show_bug.cgi?id=216216

Bad commit:

commit 3b604ca81202eea2a917eb6491e90f610fba0ec7
Author: John Ogness <john.ogness@linutronix.de>
Date: Thu Apr 21 23:28:46 2022 +0206

printk: add pr_flush()

Provide a might-sleep function to allow waiting for console
printers
to catch up to the latest logged message.

Use pr_flush() whenever it is desirable to get buffered messages
printed before continuing: suspend_console(), resume_console(),
console_stop(), console_start(), console_unblank().

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link:
https://lore.kernel.org/r/20220421212250.565456-12-john.ogness@linutronix.de

include/linux/printk.h | 7 +++++
kernel/printk/printk.c | 83
++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 90 insertions(+)