Date:   Thu, 28 May 2020 16:08:31 -0700
From:   Atish Patra <atishp@...shpatra.org>
To:     Anup Patel <anup.patel@....com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>,
        Anup Patel <anup@...infault.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v5 1/6] RISC-V: self-contained IPI handling routine

On Thu, May 21, 2020 at 6:34 AM Anup Patel <anup.patel@....com> wrote:
>
> Currently, the IPI handling routine riscv_software_interrupt() does
> not take any argument and also does not perform irq_enter()/irq_exit().
>
> This patch makes IPI handling routine more self-contained by:
> 1. Passing "pt_regs *" argument
> 2. Explicitly doing irq_enter()/irq_exit()
> 3. Explicitly save/restore "pt_regs *" using set_irq_regs()
>
> With above changes, IPI handling routine does not depend on caller
> function to perform irq_enter()/irq_exit() and save/restore of
> "pt_regs *" hence its more self-contained. This also enables us
> to call IPI handling routine from IRQCHIP drivers.
>
> Signed-off-by: Anup Patel <anup.patel@....com>
> ---
>  arch/riscv/include/asm/irq.h |  1 -
>  arch/riscv/include/asm/smp.h |  3 +++
>  arch/riscv/kernel/irq.c      | 16 ++++++++++------
>  arch/riscv/kernel/smp.c      | 11 +++++++++--
>  4 files changed, 22 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/include/asm/irq.h b/arch/riscv/include/asm/irq.h
> index 6e1b0e0325eb..0183e15ace66 100644
> --- a/arch/riscv/include/asm/irq.h
> +++ b/arch/riscv/include/asm/irq.h
> @@ -13,7 +13,6 @@
>  #define NR_IRQS         0
>
>  void riscv_timer_interrupt(void);
> -void riscv_software_interrupt(void);
>
>  #include <asm-generic/irq.h>
>
> diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
> index f4c7cfda6b7f..40bb1c15a731 100644
> --- a/arch/riscv/include/asm/smp.h
> +++ b/arch/riscv/include/asm/smp.h
> @@ -28,6 +28,9 @@ void show_ipi_stats(struct seq_file *p, int prec);
>  /* SMP initialization hook for setup_arch */
>  void __init setup_smp(void);
>
> +/* Called from C code, this handles an IPI. */
> +void handle_IPI(struct pt_regs *regs);
> +
>  /* Hook for the generic smp_call_function_many() routine. */
>  void arch_send_call_function_ipi_mask(struct cpumask *mask);
>
> diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
> index 345c4f2eba13..bb0bfcd537e7 100644
> --- a/arch/riscv/kernel/irq.c
> +++ b/arch/riscv/kernel/irq.c
> @@ -19,12 +19,15 @@ int arch_show_interrupts(struct seq_file *p, int prec)
>
>  asmlinkage __visible void __irq_entry do_IRQ(struct pt_regs *regs)
>  {
> -       struct pt_regs *old_regs = set_irq_regs(regs);
> +       struct pt_regs *old_regs;
>
> -       irq_enter();
>         switch (regs->cause & ~CAUSE_IRQ_FLAG) {
>         case RV_IRQ_TIMER:
> +               old_regs = set_irq_regs(regs);
> +               irq_enter();
>                 riscv_timer_interrupt();
> +               irq_exit();
> +               set_irq_regs(old_regs);
>                 break;
>  #ifdef CONFIG_SMP
>         case RV_IRQ_SOFT:
> @@ -32,19 +35,20 @@ asmlinkage __visible void __irq_entry do_IRQ(struct pt_regs *regs)
>                  * We only use software interrupts to pass IPIs, so if a non-SMP
>                  * system gets one, then we don't know what to do.
>                  */
> -               riscv_software_interrupt();
> +               handle_IPI(regs);
>                 break;
>  #endif
>         case RV_IRQ_EXT:
> +               old_regs = set_irq_regs(regs);
> +               irq_enter();
>                 handle_arch_irq(regs);
> +               irq_exit();
> +               set_irq_regs(old_regs);
>                 break;
>         default:
>                 pr_alert("unexpected interrupt cause 0x%lx", regs->cause);
>                 BUG();
>         }
> -       irq_exit();
> -
> -       set_irq_regs(old_regs);
>  }
>
>  void __init init_IRQ(void)
> diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
> index a65a8fa0c22d..b1d4f452f843 100644
> --- a/arch/riscv/kernel/smp.c
> +++ b/arch/riscv/kernel/smp.c
> @@ -123,11 +123,14 @@ static inline void clear_ipi(void)
>                 clint_clear_ipi(cpuid_to_hartid_map(smp_processor_id()));
>  }
>
> -void riscv_software_interrupt(void)
> +void handle_IPI(struct pt_regs *regs)
>  {
> +       struct pt_regs *old_regs = set_irq_regs(regs);
>         unsigned long *pending_ipis = &ipi_data[smp_processor_id()].bits;
>         unsigned long *stats = ipi_data[smp_processor_id()].stats;
>
> +       irq_enter();
> +
>         clear_ipi();
>
>         while (true) {
> @@ -138,7 +141,7 @@ void riscv_software_interrupt(void)
>
>                 ops = xchg(pending_ipis, 0);
>                 if (ops == 0)
> -                       return;
> +                       goto done;
>
>                 if (ops & (1 << IPI_RESCHEDULE)) {
>                         stats[IPI_RESCHEDULE]++;
> @@ -160,6 +163,10 @@ void riscv_software_interrupt(void)
>                 /* Order data access and bit testing. */
>                 mb();
>         }
> +
> +done:
> +       irq_exit();
> +       set_irq_regs(old_regs);
>  }
>
>  static const char * const ipi_names[] = {
> --
> 2.25.1
>
>

Reviewed-by: Atish Patra <atish.patra@....com>

-- 
Regards,
Atish

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