linux-kernel - Re: [PATCH v2 1/2] irqchip/riscv-imsic: Restore the IMSIC registers

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Message-ID: <CAKddAkBfBn7TPWB_nbSbPzH+Rgjcci1N4wR3FJ8kxh2QCTWQEw@mail.gmail.com>
Date: Fri, 15 Aug 2025 10:18:34 +0800
From: Nick Hu <nick.hu@...ive.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: anup@...infault.org, Alexandre Ghiti <alex@...ti.fr>, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>
Subject: Re: [PATCH v2 1/2] irqchip/riscv-imsic: Restore the IMSIC registers

On Wed, Aug 6, 2025 at 8:08 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> On Wed, Aug 06 2025 at 16:27, Nick Hu wrote:
>
> "Restore the IMSIC registers" does not tell me anything useful. When are
> they restored?
>
I’ll update it to: “Preserve the IMSIC states after PM”

> > When the system woken up from the low power state, the IMSIC might be in
>
> is woken up from a low power state
>
> > the reset state.
>
> The real important information is:
>
>    When the system enters a low power state the IMSIC might be reset,
>    but on exit nothing restores the registers, which prevents interrupt
>    delivery.
>
> Or something like that.
>
> > Therefore adding the CPU PM callbacks to restore the IMSIC register
> > when the cpu resume from the low power state.
>
> This is not a valid sentence.
>
>   Solve this by registering a CPU power management notifier, which
>   restores the IMSIC on exit.
>
> Or such.
>
> See
>
> https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#changelog
>
> for further explanation.
>
I'll correct it in the next version. Thanks.

> > diff --git a/drivers/irqchip/irq-riscv-imsic-early.c b/drivers/irqchip/irq-riscv-imsic-early.c
> > index d9ae87808651..62bcbcae8bd4 100644
> > --- a/drivers/irqchip/irq-riscv-imsic-early.c
> > +++ b/drivers/irqchip/irq-riscv-imsic-early.c
> > @@ -7,6 +7,7 @@
> >  #define pr_fmt(fmt) "riscv-imsic: " fmt
> >  #include <linux/acpi.h>
> >  #include <linux/cpu.h>
> > +#include <linux/cpu_pm.h>
> >  #include <linux/interrupt.h>
>
> This does neither apply against Linus tree nor against tip
>
> > -static int imsic_starting_cpu(unsigned int cpu)
> > +static void imsic_restore(void)
>
> This function is used for both setup _and_ restore, so naming it
> restore() is misleading at best.
>
Will rename it to imsic_regs_init()

> >  {
> > -     /* Mark per-CPU IMSIC state as online */
> > -     imsic_state_online();
> > -
> > -     /* Enable per-CPU parent interrupt */
> > -     enable_percpu_irq(imsic_parent_irq, irq_get_trigger_type(imsic_parent_irq));
> > -
> >       /* Setup IPIs */
> >       imsic_ipi_starting_cpu();
> >
> > @@ -128,6 +123,19 @@ static int imsic_starting_cpu(unsigned int cpu)
> >
> >       /* Enable local interrupt delivery */
> >       imsic_local_delivery(true);
> > +}
> > +
> > +static int imsic_starting_cpu(unsigned int cpu)
> > +{
> > +     /* Mark per-CPU IMSIC state as online */
> > +     imsic_state_online();
> > +
> > +     /* Enable per-CPU parent interrupt */
> > +     enable_percpu_irq(imsic_parent_irq,
> > +                       irq_get_trigger_type(imsic_parent_irq));
>
> No line break required. You have 100 characters.
>
> > +
> > +     /* Restore the imsic reg */
>
> One IMSIC register? Can you please write proper sentences and write
> words out? This is not twitter. Also use IMSIC uppercase as the rest of
> the code does in the comments.
>
Sorry, I’ll be more careful.

> Thanks,
>
>         tglx