Re: [PATCH tty 1/1] serial: 8250: Change console_msr_work to IRQ_WORK_LAZY

[John Ogness]

On 2026-08-28, Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote:
> On 2026-08-28 18:04:08 [+0206], John Ogness wrote:
>> For some platforms it is a problem to queue irq_work when entering
>> cpuidle states. Since irq_work is used for deferred MSR handling,
>> any atomic console printing when entering cpuidle states can lead
>> to the affected hardware hanging. Tegra20 and Tegra30 are examples
>> of such platforms. Avoiding raising the irq_work IRQ has shown to
>> circumvent the problem.
>
> I would argue that this is done for the benefit of less interrupts since
> there no need to handle console_msr_work immediately.

Indeed that is a better argument, but strictly speaking, it isn't the
motivation. I think it is important to clarify that _currently_ there is
a problem that the explicit lazy is working around.

I expect most irq_work users could be changed to lazy with the argument
of reducing interrupts.

> side-note: Wasn't there another tegra workaround in v5/take1?

Yes, related to suspend/resume, implemented at the printk level [0]. Now
that we better understand the problem, that could be reverted. However,
it also provided a side-effect benefit: switching to atomic mode on
suspend when no_console_suspend is specified. I suppose at some point
(once the nbcon churn settles down) we will clean those changes so that
the naming and semantics really focus on "switching to atomic" rather
than "block irqwork".

John

[0] https://lore.kernel.org/lkml/20251113160351.113031-3-john.ogness@xxxxxxxxxxxxx