Re: [PATCH v6 03/14] drivers: irqchip/riscv-intc: Mark all INTC nodes as initialized

[Anup Patel]

On Thu, Jul 20, 2023 at 3:45 AM Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
>
> On Wed, Jul 19, 2023 at 4:36 AM Anup Patel <apatel@xxxxxxxxxxxxxxxx> wrote:
> >
> > The RISC-V INTC local interrupts are per-HART (or per-CPU) so
> > we create INTC IRQ domain only for the INTC node belonging to
> > the boot HART. This means only the boot HART INTC node will be
> > marked as initialized and other INTC nodes won't be marked which
> > results downstream interrupt controllers (such as IMSIC and APLIC
> > direct-mode) not being probed due to missing device suppliers.
> >
> > To address this issue, we mark all INTC node for which we don't
> > create IRQ domain as initialized.
> >
> > Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> > ---
> >  drivers/irqchip/irq-riscv-intc.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/irqchip/irq-riscv-intc.c b/drivers/irqchip/irq-riscv-intc.c
> > index 65f4a2afb381..4e2704bc25fb 100644
> > --- a/drivers/irqchip/irq-riscv-intc.c
> > +++ b/drivers/irqchip/irq-riscv-intc.c
> > @@ -155,8 +155,16 @@ static int __init riscv_intc_init(struct device_node *node,
> >          * for each INTC DT node. We only need to do INTC initialization
> >          * for the INTC DT node belonging to boot CPU (or boot HART).
> >          */
> > -       if (riscv_hartid_to_cpuid(hartid) != smp_processor_id())
> > +       if (riscv_hartid_to_cpuid(hartid) != smp_processor_id()) {
> > +               /*
> > +                * The INTC nodes of each CPU are suppliers for downstream
> > +                * interrupt controllers (such as IMSIC and APLIC direct-mode)
> > +                * so we should mark an INTC node as initialized if we are
> > +                * not creating IRQ domain for it.
> > +                */
>
> I'm a bit confused by this. If those non-boot CPUs INTC doesn't have
> an IRQ domain, why are the downstream interrupt controllers listing
> these non-boot CPU INTCs as an upstream interrupt controller?

Downstream interrupt controllers (such as PLIC, APLIC direct-mode,
or IMSIC) use "interrupts-extended" DT property to associate their
MMIO resources with target CPU.

For example: If we have 4 CPUs then PLIC will typically have 2 PLIC
MMIO contexts for each CPU where one context is for M-mode and
another context is for S-mode. In this case, there are total 8 PLIC
MMIO contexts and the arrangement of these MMIO resources is
platform specific so "interrupts-extended" DT property is used by
PLIC driver to discover the arrangement of PLIC MMIO contexts
and their mapping to target CPU.

Similar to the above example, the APLIC direct-mode has per-CPU
IDC MMIO registers and "interrupts-extended" DT property is used
to discover arrangement of these IDC MMIO registers and their
mapping to the target CPU.

>
> This is more of a question of the existing behavior that this patch,
> but this patch highlights the existing oddity.
>
> -Saravana
>
> > +               fwnode_dev_initialized(of_fwnode_handle(node), true);
> >                 return 0;
> > +       }
> >
> >         return riscv_intc_init_common(of_node_to_fwnode(node));
> >  }
> > --
> > 2.34.1
> >

Regards,
Anup