Re: [PATCH printk] printk/nbcon: Change nbcon_irq_work to IRQ_WORK_LAZY

[Petr Mladek]

On Thu 2026-08-27 20:53:38, John Ogness wrote:
> For some platforms it is a problem to queue irq_work when entering
> cpuidle states. Since nbcon uses irq_work for waking the printing
> kthreads, any printk() calls 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.
> 
> Change the nbcon_irq_work to be IRQ_WORK_LAZY, thus not raising
> an IRQ upon irq_work queuing. The irq_work is then handled on the
> next interrupt (worst case, kernel tick). This additional delay is
> acceptable because nbcon_irq_work is only responsible for
> non-emergency deferred printing, which is delayed anyway. This also
> has the benefit of not needing to raise an IRQ for each printk()
> call.
> 
> Link: https://lore.kernel.org/lkml/f3757a75-0ba1-4558-bf57-f19ab7e59a4c@xxxxxxxxxx
> Fixes: 76f258bf3f2a ("printk: nbcon: Introduce printer kthreads")
> Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>

Looks good to me:

Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>

I am going to wait for v2 which would fix the preexisting problem
reported by Sashiko. Anyway, I am going to queue this for 7.3-rcX
to prevent regressions caused by converting the uart 8250 console
driver into nbcon API.

Best Regards,
Petr