Debugging a box via serial console


I’m trying to debug via a serial console a suspend problem I’m having with kernel 5.15 (not with 5.14.x) on F35
with 5.14 suspend shuts the box off as usual.
with 5.15 suspend hangs the box hard; no ping. only a hard reset gets it to live again

the serial console is running.
I can login to the box I want to debug and see the boot messages.

But what I can’t see/log is all what the kernel does after I type

sudo systemctl suspend

my /etc/default/grub:

GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"

# serial console
GRUB_CMDLINE_LINUX="console=tty0 console=tty1 console=ttyS0,115200 systemd.log_level=debug systemd.log_target=console" 

Idea’s ?

- bump -

I’m still not sure about the serial console settings, but the cause of unable to suspend with 5.15.y seems to be the Wifi/BT driver (Intel(R) Wi-Fi 6 AX201 160MHz, REV=0x354)

mainboard is:

I bump back :wink: 5.14.16 is out, did you test it?

Sorry … missed the .14 in between hehe

AFAIK, there isn’t even a 5.16-rc1 from (might released tonight though), while for rawhide there is a *-rc0.
Anyway that kernels (might) contain(s) a lot of bugs in that early state…

the problem I’m having seems to be a regression from 5.14 and might hit more people when Fedora 35 jumps to kernel 5.15, so it should be investigated/fixed before.

therefore I/one need to provide some nice debug log’s so the developer could know where to look at. My vague bet is: it’s around PCIe …

AFAIK, best to get debug log’s is via serial console so I need to get that correct working before

Do you need to add no_console_suspend as a kernel parameter?

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yup, that’s it !
with the following I could see what the box is doing during suspend

it seems to be sufficing if “GRUB_CMDLINE_LINUX” is only this one:

GRUB_CMDLINE_LINUX=“console=tty0 console=tty1 console=ttyS0,115200 systemd.log_level=debug no_console_suspend”

the additional “systemd.log_target=console” is floating the output (to much)

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