Re: [PATCH v2 2/6] irqchip/riscv-intc: Create domain using named fwnode

[Anup Patel <anup@brainfault.org>]

On Thu, Feb 17, 2022 at 8:42 PM Marc Zyngier <maz@kernel.org> wrote:
>
> On 2022-01-28 05:25, Anup Patel wrote:
> > We should create INTC domain using a synthetic fwnode which will allow
> > drivers (such as RISC-V SBI IPI driver, RISC-V timer driver, RISC-V
> > PMU driver, etc) not having dedicated DT/ACPI node to directly create
> > interrupt mapping for standard local interrupt numbers defined by the
> > RISC-V privileged specification.
> >
> > Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> > ---
> >  arch/riscv/include/asm/irq.h      |  2 ++
> >  arch/riscv/kernel/irq.c           | 13 +++++++++++++
> >  drivers/clocksource/timer-clint.c | 13 +++++++------
> >  drivers/clocksource/timer-riscv.c | 11 ++---------
> >  drivers/irqchip/irq-riscv-intc.c  | 12 ++++++++++--
> >  drivers/irqchip/irq-sifive-plic.c | 19 +++++++++++--------
> >  6 files changed, 45 insertions(+), 25 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/irq.h
> > b/arch/riscv/include/asm/irq.h
> > index e4c435509983..f85ebaf07505 100644
> > --- a/arch/riscv/include/asm/irq.h
> > +++ b/arch/riscv/include/asm/irq.h
> > @@ -12,6 +12,8 @@
> >
> >  #include <asm-generic/irq.h>
> >
> > +extern struct fwnode_handle *riscv_intc_fwnode(void);
> > +
> >  extern void __init init_IRQ(void);
> >
> >  #endif /* _ASM_RISCV_IRQ_H */
> > diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
> > index 7207fa08d78f..f2fed78ab659 100644
> > --- a/arch/riscv/kernel/irq.c
> > +++ b/arch/riscv/kernel/irq.c
> > @@ -7,9 +7,22 @@
> >
> >  #include <linux/interrupt.h>
> >  #include <linux/irqchip.h>
> > +#include <linux/irqdomain.h>
> > +#include <linux/module.h>
> >  #include <linux/seq_file.h>
> >  #include <asm/smp.h>
> >
> > +static struct fwnode_handle *intc_fwnode;
> > +
> > +struct fwnode_handle *riscv_intc_fwnode(void)
> > +{
> > +     if (!intc_fwnode)
> > +             intc_fwnode = irq_domain_alloc_named_fwnode("RISCV-INTC");
> > +
> > +     return intc_fwnode;
> > +}
> > +EXPORT_SYMBOL_GPL(riscv_intc_fwnode);
>
> Why is this created outside of the root interrupt controller driver?
> Furthermore, why do you need to create a new fwnode the first place?
> As far as I can tell, the INTC does have a node, and what you don't
> have is the firmware linkage between PMU (an others) and the INTC.

Fair enough, I will update this patch to not create a synthetic fwnode.

The issue is not with INTC driver. We have other drivers and places
(such as SBI IPI driver, SBI PMU driver, and KVM RISC-V AIA support)
where we don't have a way to locate INTC fwnode.

>
> what you should have instead is something like:
>
> static struct fwnode_handle *(*__get_root_intc_node)(void);
> struct fwnode_handle *riscv_get_root_intc_hwnode(void)
> {
>          if (__get_root_intc_node)
>                  return __get_root_intc_node();
>
>          return NULL;
> }
>
> and the corresponding registration interface.

Thanks, I will follow this suggestion. This is a much better approach
and it will avoid touching existing drivers.

>
> But either way, something breaks: the INTC has one node per CPU, and
> expect one irqdomain per CPU. Having a single fwnode completely breaks
> the INTC driver (and probably the irqdomain list, as we don't check for
> duplicate entries).
>
> > diff --git a/drivers/irqchip/irq-riscv-intc.c
> > b/drivers/irqchip/irq-riscv-intc.c
> > index b65bd8878d4f..26ed62c11768 100644
> > --- a/drivers/irqchip/irq-riscv-intc.c
> > +++ b/drivers/irqchip/irq-riscv-intc.c
> > @@ -112,8 +112,16 @@ static int __init riscv_intc_init(struct
> > device_node *node,
> >       if (riscv_hartid_to_cpuid(hartid) != smp_processor_id())
> >               return 0;
> >
> > -     intc_domain = irq_domain_add_linear(node, BITS_PER_LONG,
> > -                                         &riscv_intc_domain_ops, NULL);
> > +     /*
> > +      * Create INTC domain using a synthetic fwnode which will allow
> > +      * drivers (such as RISC-V SBI IPI driver, RISC-V timer driver,
> > +      * RISC-V PMU driver, etc) not having dedicated DT/ACPI node to
> > +      * directly create interrupt mapping for standard local interrupt
> > +      * numbers defined by the RISC-V privileged specification.
> > +      */
> > +     intc_domain = irq_domain_create_linear(riscv_intc_fwnode(),
> > +                                            BITS_PER_LONG,
> > +                                            &riscv_intc_domain_ops, NULL);
>
> This is what I'm talking about. It is simply broken. So either you don't
> need a per-CPU node (and the DT was bad the first place), or you
> absolutely need
> one (and the whole 'well-known/default domain' doesn't work at all).
>
> Either way, this patch is plain wrong.

Okay, I will update this patch with the new approach which you suggested.

Regards,
Anup

>
>
>          M.
> --
> Jazz is not dead. It just smells funny...