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

[Jon Hunter]

On 27/08/2026 10:45, Thierry Reding wrote:
> 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?
By default 'nvidia,suspend-mode' is set to 1 for this board. In order,
to disable CPU idle CC6 state (CPU cluster off) I needed to remove this
property completely. Doing so does work around the problem and the
device boots.

Similarly, if I make the following change to ensure that CC6 is
disabled for Tegra20 and Tegra30 this also works for both Tegra20 and
Tegra30 ...

diff --git a/drivers/cpuidle/cpuidle-tegra.c b/drivers/cpuidle/cpuidle-tegra.c
index aca907a62bb5..d592e1f37f00 100644
--- a/drivers/cpuidle/cpuidle-tegra.c
+++ b/drivers/cpuidle/cpuidle-tegra.c
@@ -374,9 +374,11 @@ static int tegra_cpuidle_probe(struct platform_device *pdev)
        case TEGRA20:
                /* Tegra20 isn't capable to power-off individual CPU cores */
                tegra_cpuidle_disable_state(TEGRA_C7);
+               tegra_cpuidle_disable_state(TEGRA_CC6);
                break;
 
        case TEGRA30:
+               tegra_cpuidle_disable_state(TEGRA_CC6);
                break;
 
        case TEGRA114:

Jon

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nvpublic