linux-kernel - Re: [RFC PATCH 2/4] irqchip/riscv-intc: Support large non-standard hwirq number

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Message-ID: <ZP7L_ahJOBXnCSP7@APC323>
Date:   Mon, 11 Sep 2023 16:12:45 +0800
From:   Yu-Chien Peter Lin <peterlin@...estech.com>
To:     Anup Patel <anup@...infault.org>
CC:     <linux-riscv@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
        <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <conor.dooley@...rochip.com>,
        <atishp@...shpatra.org>, <prabhakar.mahadev-lad.rj@...renesas.com>,
        <ajones@...tanamicro.com>, <heiko@...ech.de>,
        <samuel@...lland.org>, <geert+renesas@...der.be>,
        <n.shubin@...ro.com>, <dminus@...estech.com>,
        <ycliang@...estech.com>, <tim609@...estech.com>,
        <locus84@...estech.com>, <dylan@...estech.com>
Subject: Re: [RFC PATCH 2/4] irqchip/riscv-intc: Support large non-standard
 hwirq number

On Thu, Sep 07, 2023 at 06:36:52PM +0530, Anup Patel wrote:
> On Thu, Sep 7, 2023 at 7:48 AM Yu Chien Peter Lin
> <peterlin@...estech.com> wrote:
> >
> > Currently, the implementation of the RISC-V INTC driver uses the
> > interrupt cause as hwirq and has a limitation of supporting a
> > maximum of 64 hwirqs. However, according to the privileged spec,
> > interrupt cause >= 16 are defined for platform use.
> >
> > This limitation prevents us from fully utilizing the available
> > local interrupt sources. Additionally, the hwirqs used on RISC-V
> > are sparse, with only interrupt numbers 1, 5 and 9 (plus Sscofpmf
> > or T-Head's PMU irq) being currently used for supervisor mode.
> >
> > The patch switches to using irq_domain_create_tree() which
> > creates the radix tree map, allowing us to handle a larger
> > number of hwirqs.
> >
> > Signed-off-by: Yu Chien Peter Lin <peterlin@...estech.com>
> > Reviewed-by: Charles Ci-Jyun Wu <dminus@...estech.com>
> > Reviewed-by: Leo Yu-Chi Liang <ycliang@...estech.com>
> >
> > ---
> > There are 3 hwirqs of local interrupt source exceed 64 defined in
> > AX45MP datasheet [1] Table 56: AX45MP-1C scause Value After Trap:
> > - 256+16 Slave port ECC error interrupt (S-mode)
> > - 256+17 Bus write transaction error interrupt (S-mode)
> > - 256+18 Performance monitor overflow interrupt(S-mode)
> >
> > [1] http://www.andestech.com/wp-content/uploads/AX45MP-1C-Rev.-5.0.0-Datasheet.pdf
> > ---
> >  drivers/irqchip/irq-riscv-intc.c | 10 ++++------
> >  1 file changed, 4 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/irqchip/irq-riscv-intc.c b/drivers/irqchip/irq-riscv-intc.c
> > index 4adeee1bc391..76e1229c45de 100644
> > --- a/drivers/irqchip/irq-riscv-intc.c
> > +++ b/drivers/irqchip/irq-riscv-intc.c
> > @@ -24,8 +24,8 @@ static asmlinkage void riscv_intc_irq(struct pt_regs *regs)
> >  {
> >         unsigned long cause = regs->cause & ~CAUSE_IRQ_FLAG;
> >
> > -       if (unlikely(cause >= BITS_PER_LONG))
> > -               panic("unexpected interrupt cause");
> > +       if (!irq_find_mapping(intc_domain, cause))
> > +               panic("unexpected interrupt cause: %ld", cause);
> 
> Checking irq_find_mapping() is redundant here instead check the return
> value of generic_handle_domain_irq() and print warning on error.
> 
> >
> >         generic_handle_domain_irq(intc_domain, cause);
> >  }
> > @@ -117,8 +117,8 @@ static int __init riscv_intc_init_common(struct fwnode_handle *fn)
> >  {
> >         int rc;
> >
> > -       intc_domain = irq_domain_create_linear(fn, BITS_PER_LONG,
> > -                                              &riscv_intc_domain_ops, NULL);
> > +       intc_domain = irq_domain_create_tree(fn, &riscv_intc_domain_ops,
> > +                                            NULL);
> 
> This is incomplete because you have additional customization on-top-of
> vanilla RISC-V INTC.
> 
> I suggest to do the following:
> 1) Define an enum of types of INTC (such as generic, andestech, etc)
> 2) Define new compatible string "andestec,cpu-intc" for you custom INTC
>     and pass that information to riscv_intc_init_common()
> 3) Extend riscv_intc_domain_map() to use custom andestech_intc_chip
>     for the custom local irqs. The andestech_intc_chip will provide andes
>     specific mask/unmask mechanism.

Hi Anup,

Sure, we will introduce the Andes INTC for a custom IRQ chip.

Thanks,
Peter Lin

> >         if (!intc_domain) {
> >                 pr_err("unable to add IRQ domain\n");
> >                 return -ENXIO;
> > @@ -132,8 +132,6 @@ static int __init riscv_intc_init_common(struct fwnode_handle *fn)
> >
> >         riscv_set_intc_hwnode_fn(riscv_intc_hwnode);
> >
> > -       pr_info("%d local interrupts mapped\n", BITS_PER_LONG);
> > -
> >         return 0;
> >  }
> >
> > --
> > 2.34.1
> >
> 
> Regards,
> Anup