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

[Jon Hunter <jonathanh@nvidia.com>]

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@suse.com> 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

-- 
nvpublic