Re: [PATCH tty v11 1/2] serial: 8250: Switch to nbcon console, take 2

[Thierry Reding]

On Thu, Aug 20, 2026 at 01:26:03PM +0206, John Ogness wrote:
> On 2026-08-18, Petr Mladek <pmladek@xxxxxxxx> wrote:
> >> [0] https://pastebin.com/FhQVSqfy
> 
> ...
> 
> > Almost everything works as expected except for:
> >
> >   1. I am not sure why "printk: console [ttyS0] disabled" is printed.
> >      It does not make any sense to me.
> 
> I have seen this in the past. It can happens unregister_console_locked()
> has always printed the disabled message before actually checking if the
> console is registered.
> 
> IIRC it has something to do with serial8250_register_8250_port() calling
> uart_remove_one_port(). I remember starting to look into how to fix it
> but then was going down a rabbit hole that exceeded my scope at the
> time.
> 
> >   2. The WARNING would be handled with NBCON_PRIO_EMERGENCY.
> >      I wonder if this warning happened also with "v5" of this
> >      patchset.
> 
> The tegra issue we had with v5 was related to irqwork being scheduled
> when suspending. When keep_bootcon is specified, there will be no
> irqwork scheduled during boot because legacy_direct=true.
> 
> From the backtrace in the posted boot log we see that the warning is
> within tegra_pmc_enter_suspend_mode(). I am wondering if this is the
> same issue we saw with v5... an irqwork getting scheduled when the tegra
> is entering some suspend state.

You mentioning tegra_pmc_enter_suspend_mode() jogged a memory. We have
to play some weird cpuidle tricks when PCI interrupts are anebled
because of a hardware bug. That bug, as far as I know, is only Tegra20
specific, so it doesn't explain this. In this particular case we're also
not talking about PCI in this case, *but* I wonder if there's maybe
other IRQ issues related to cpuidle.

It's a bit of a shot in the dark, but we could try disabling the various
suspend modes via the PMC DT node. Notably LP2 seems to be the one
that's causing issues on Tegra20 with PCI, so maybe changing
nvidia,suspend-mode to something like 0 or 1 would help narrow things
down?

Thierry

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