linux-kernel - Re: [PATCH v2 04/17] ARM: Allow IPIs to be handled as normal interrupts

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Message-ID: <jhjk0zvgfz7.mognet@arm.com>
Date:   Thu, 25 Jun 2020 19:25:32 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Sumit Garg <sumit.garg@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>, kernel-team@...roid.com
Subject: Re: [PATCH v2 04/17] ARM: Allow IPIs to be handled as normal interrupts


On 24/06/20 20:57, Marc Zyngier wrote:
> @@ -696,9 +696,76 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
>
>       if ((unsigned)ipinr < NR_IPI)
>               trace_ipi_exit_rcuidle(ipi_types[ipinr]);
> +}
> +
> +/* Legacy version, should go away once all irqchips have been converted */
> +void handle_IPI(int ipinr, struct pt_regs *regs)
> +{
> +	struct pt_regs *old_regs = set_irq_regs(regs);
> +
> +	irq_enter();
> +	do_handle_IPI(ipinr);
> +	irq_exit();
> +
>       set_irq_regs(old_regs);
>  }
>
> +static irqreturn_t ipi_handler(int irq, void *data)
> +{
> +	do_handle_IPI(irq - ipi_irq_base);
> +	return IRQ_HANDLED;
> +}
> +
> +static void ipi_send(const struct cpumask *target, unsigned int ipi)
> +{
> +	__ipi_send_mask(ipi_desc[ipi], target);
> +}
> +
> +static void ipi_setup(int cpu)
> +{
> +	if (ipi_irq_base) {
> +		int i;
> +
> +		for (i = 0; i < nr_ipi; i++)
> +			enable_percpu_irq(ipi_irq_base + i, 0);
> +	}
> +}
> +
> +static void ipi_teardown(int cpu)
> +{
> +	if (ipi_irq_base) {
> +		int i;
> +
> +		for (i = 0; i < nr_ipi; i++)
> +			disable_percpu_irq(ipi_irq_base + i);
> +	}
> +}
> +
> +void __init set_smp_ipi_range(int ipi_base, int n)
> +{
> +	int i;
> +
> +	WARN_ON(n < MAX_IPI);
> +	nr_ipi = min(n, MAX_IPI);


I got confused by that backtrace thing and NR_IPI vs MAX_IPI.
I think I got it now : we don't want to call trace_ipi_raise() for
IPI_CPU_BACKTRACE *but* we still need to alloc the desc and route it
through the generic IPI layers.

The only difference I can tell is that now we will get some trace events
for it via the handler entry/exit tracepoints - that shouldn't cause any
issue.

> +
> +	for (i = 0; i < nr_ipi; i++) {
> +		int err;
> +
> +		err = request_percpu_irq(ipi_base + i, ipi_handler,
> +					 "IPI", &irq_stat);
> +		WARN_ON(err);
> +
> +		ipi_desc[i] = irq_to_desc(ipi_base + i);
> +		irq_set_status_flags(ipi_base + i, IRQ_HIDDEN);
> +	}
> +
> +	ipi_irq_base = ipi_base;
> +	set_smp_cross_call(ipi_send);
> +
> +	/* Setup the boot CPU immediately */
> +	ipi_setup(smp_processor_id());
> +}
> +
>  void smp_send_reschedule(int cpu)
>  {
>       smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE);