Re: [PATCH v13 4/7] RISC-V: Treat IPIs as normal Linux IRQs

[Marc Zyngier]

On Tue, 29 Nov 2022 14:24:46 +0000,
Anup Patel <apatel@xxxxxxxxxxxxxxxx> wrote:
> 
> 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@xxxxxxxxxxxxxxxx>
> ---
>  arch/riscv/Kconfig                |   2 +
>  arch/riscv/include/asm/sbi.h      |  10 +-
>  arch/riscv/include/asm/smp.h      |  35 ++++---
>  arch/riscv/kernel/Makefile        |   1 +
>  arch/riscv/kernel/cpu-hotplug.c   |   3 +-
>  arch/riscv/kernel/irq.c           |   3 +-
>  arch/riscv/kernel/sbi-ipi.c       |  81 ++++++++++++++++
>  arch/riscv/kernel/sbi.c           | 106 +++-----------------
>  arch/riscv/kernel/smp.c           | 155 +++++++++++++++---------------
>  arch/riscv/kernel/smpboot.c       |   5 +-
>  drivers/clocksource/timer-clint.c |  65 ++++++++++---
>  drivers/irqchip/Kconfig           |   1 +
>  drivers/irqchip/irq-riscv-intc.c  |  55 +++++------
>  13 files changed, 287 insertions(+), 235 deletions(-)
>  create mode 100644 arch/riscv/kernel/sbi-ipi.c
>

[...]

> diff --git a/arch/riscv/kernel/sbi-ipi.c b/arch/riscv/kernel/sbi-ipi.c
> new file mode 100644
> index 000000000000..6466706b03a7
> --- /dev/null
> +++ b/arch/riscv/kernel/sbi-ipi.c
> @@ -0,0 +1,81 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Multiplex several IPIs over a single HW IPI.
> + *
> + * Copyright (c) 2022 Ventana Micro Systems Inc.
> + */
> +
> +#define pr_fmt(fmt) "riscv: " fmt
> +#include <linux/cpu.h>
> +#include <linux/init.h>
> +#include <linux/irq.h>
> +#include <linux/irqdomain.h>
> +#include <linux/percpu.h>
> +#include <asm/sbi.h>
> +
> +static int sbi_ipi_virq;
> +static DEFINE_PER_CPU_READ_MOSTLY(int, sbi_ipi_dummy_dev);
> +
> +static irqreturn_t sbi_ipi_handle(int irq, void *dev_id)
> +{
> +	csr_clear(CSR_IP, IE_SIE);
> +	ipi_mux_process();
> +	return IRQ_HANDLED;

Urgh... I really wish I hadn't seen this. This requires a chained
handler. You had it before, and yet you dropped it. Why?

Either you call ipi_mux_process() from your root interrupt controller,
or you implement a chained handler. But not this.

Same thing about the clint stuff.

	M.

-- 
Without deviation from the norm, progress is not possible.