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

[John Ogness <john.ogness@linutronix.de>]

Hi Jon,

On 2026-08-27, Jon Hunter <jonathanh@nvidia.com> wrote:
>> diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
>> index a5921a84a80ed..ad79e30afd647 100644
>> --- a/kernel/printk/nbcon.c
>> +++ b/kernel/printk/nbcon.c
>> @@ -1782,7 +1782,7 @@ bool nbcon_alloc(struct console *con)
>>   	}
>>   
>>   	rcuwait_init(&con->rcuwait);
>> -	init_irq_work(&con->irq_work, nbcon_irq_work);
>> +	con->irq_work = IRQ_WORK_INIT_LAZY(nbcon_irq_work);
>>   	atomic_long_set(&ACCESS_PRIVATE(con, nbcon_prev_seq), -1UL);
>>   	nbcon_state_set(con, &state);
>>   
>
> I gave this a quick try on Tegra20 and Tegra30 and I can confirm that
> this does work.

OK, great. I will prepare an official patch for mainline to change
nbcon_irq_work to LAZY.

Back with v5 you reported [0] similar issues due to suspend/resume. For
that we implemented the @console_irqwork_blocked workaround. We probably
do not need that anymore. You could verify that with the following hack
(and booting with no_console_suspend). Note that you also need the LAZY
change above.

===== BEGIN SUSPEND HACK =====
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 6d3d18a50da74..73c85f6de2c9e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2796,7 +2796,6 @@ void console_suspend_all(void)
 	 * any klogd waiters are not triggered.
 	 */
 	pr_flush(1000, true);
-	console_irqwork_blocked = true;
 
 	if (!console_suspend_enabled)
 		return;
===== END SUSPEND HACK =====

However, this workaround did allow the consoles to switch to atomic mode
on suspend when no_console_suspend is specified at boot. So the
workaround might be interesting for that reason alone. But we should no
longer need it for the reasons mentioned in commit 26873e3e7f0c
("printk: Avoid scheduling irq_work on suspend")

John

[0] https://lore.kernel.org/lkml/80b020fc-c18a-4da4-b222-16da1cab2f4c@nvidia.com