linux-kernel - Re: [PATCH v8 4/7] RISC-V: Treat IPIs as normal Linux IRQs

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Message-ID: <8f4ae429-0f12-2096-c07b-fe43b3abb4fe@microchip.com>
Date:   Fri, 26 Aug 2022 18:48:42 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <apatel@...tanamicro.com>, <palmer@...belt.com>,
        <paul.walmsley@...ive.com>, <tglx@...utronix.de>, <maz@...nel.org>,
        <daniel.lezcano@...aro.org>
CC:     <atishp@...shpatra.org>, <Alistair.Francis@....com>,
        <anup@...infault.org>, <linux-riscv@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 4/7] RISC-V: Treat IPIs as normal Linux IRQs

On 20/08/2022 07:54, Anup Patel wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Currently, the RISC-V kernel provides arch specific hooks (i.e.
> struct riscv_ipi_ops) to register IPI handling methods. The stats
> gathering of IPIs is also arch specific in the RISC-V kernel.
> 
> Other architectures (such as ARM, ARM64, and MIPS) have moved away
> from custom arch specific IPI handling methods. Currently, these
> architectures have Linux irqchip drivers providing a range of Linux
> IRQ numbers to be used as IPIs and IPI triggering is done using
> generic IPI APIs. This approach allows architectures to treat IPIs
> as normal Linux IRQs and IPI stats gathering is done by the generic
> Linux IRQ subsystem.
> 
> We extend the RISC-V IPI handling as-per above approach so that arch
> specific IPI handling methods (struct riscv_ipi_ops) can be removed
> and the IPI handling is done through the Linux IRQ subsystem.
> 
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>

> +void riscv_ipi_set_virq_range(int virq, int nr)
> +{
> +       int i, err;
> 
> -               if (ops & (1 << IPI_IRQ_WORK)) {
> -                       stats[IPI_IRQ_WORK]++;
> -                       irq_work_run();
> -               }
> +       if (WARN_ON(ipi_virq_base))
> +               return;
> 
> -#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
> -               if (ops & (1 << IPI_TIMER)) {
> -                       stats[IPI_TIMER]++;
> -                       tick_receive_broadcast();
> -               }
> -#endif
> -               BUG_ON((ops >> IPI_MAX) != 0);
> +       WARN_ON(nr < IPI_MAX);
> +       nr_ipi = min(nr, IPI_MAX);
> +       ipi_virq_base = virq;
> +
> +       /* Request IPIs */
> +       for (i = 0; i < nr_ipi; i++) {
> +               err = request_percpu_irq(ipi_virq_base + i, handle_IPI,
> +                                        "IPI", &ipi_virq_base);

FWIW, ?sparse? does not like this:
arch/riscv/kernel/smp.c:163:50: warning: incorrect type in argument 4 (different address spaces)
arch/riscv/kernel/smp.c:163:50:    expected void [noderef] __percpu *percpu_dev_id
arch/riscv/kernel/smp.c:163:50:    got int *

> +               WARN_ON(err);
> 
> -               /* Order data access and bit testing. */
> -               mb();
> +               ipi_desc[i] = irq_to_desc(ipi_virq_base + i);
> +               irq_set_status_flags(ipi_virq_base + i, IRQ_HIDDEN);
>         }
> +
> +       /* Enabled IPIs for boot CPU immediately */
> +       riscv_ipi_enable();
>  }