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

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Date:   Mon, 29 Jun 2020 10:37:41 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Valentin Schneider <valentin.schneider@....com>
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 2020-06-25 19:25, Valentin Schneider wrote:
> 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.

Indeed, and I didn't want to have a bizarre "+ 1" hanging about.

> 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.

I hope so. I don't see how you can avoid all tracepoints anyway (if that
was the intention).

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...