Re: [PATCH v14 01/18] irqchip/sifive-plic: Convert PLIC driver into a platform driver

Geert Uytterhoeven
2024-05-30T07:07:12Z

Hi Samuel,

On Thu, May 30, 2024 at 12:04 AM Samuel Holland
<samuel.holland@sifive.com> wrote:
> On 2024-05-29 9:22 AM, Geert Uytterhoeven wrote:
> > On Thu, Feb 22, 2024 at 10:41 AM Anup Patel <apatel@ventanamicro.com> wrote:
> >> The PLIC driver does not require very early initialization so convert
> >> it into a platform driver.
> >>
> >> After conversion, the PLIC driver is probed after CPUs are brought-up
> >> so setup cpuhp state after context handler of all online CPUs are
> >> initialized otherwise PLIC driver crashes for platforms with multiple
> >> PLIC instances.
> >>
> >> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> >
> > Thanks for your patch, which is now commit 8ec99b033147ef3b
> > ("irqchip/sifive-plic: Convert PLIC driver into a platform
> > driver") in v6.9.
> >
> > It looks like this conversion is causing issues on BeagleV Starlight
> > Beta. After updating esmil/visionfive to v6.10-rc1, the kernel usually
> > fails to boot. Adding "earlycon keep_bootcon" reveals these differences:
> >
> > -riscv-plic c000000.interrupt-controller: mapped 133 interrupts with 2
> > handlers for 4 contexts.
> > +------------[ cut here ]------------
> > +WARNING: CPU: 0 PID: 1 at drivers/irqchip/irq-sifive-plic.c:373

> > +Unable to handle kernel NULL pointer dereference at virtual address

> The fact that you hit the warning indicates that plic_handle_irq() was called
> before handler->present was set. Previously the PLIC driver was probed very
> early, so it is unlikely that some peripheral already had a pending interrupt.
> Now, while platform device drivers would not yet be able to request interrupts
> (because the irqdomain is not registered yet), they could have programmed the
> hardware in a way that generates an interrupt. If that interrupt was enabled at
> the PLIC (e.g. by the bootloader), then we could expect plic_handle_irq() to be
> called as soon as irq_set_chained_handler() is called.
>
> So the fix is to not call irq_set_chained_handler() until after the handlers are
> completely set up.
>
> I've sent a patch doing this:
> https://lore.kernel.org/linux-riscv/20240529215458.937817-1-samuel.holland@sifive.com/

Thanks, that fixed the issue!

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds