linux-kernel - Re: [PATCH v2 2/9] drivers: irqchip: Add STM32 external interrupts support

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Message-ID: <CALszF6AKS2-SxQKTM-hrVfB2tMZS_21jRx9HtnHVACO1o=1Fgw@mail.gmail.com>
Date:	Tue, 19 Apr 2016 10:00:29 +0200
From:	Maxime Coquelin <mcoquelin.stm32@...il.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Mark Rutland <mark.rutland@....com>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Daniel Thompson <daniel.thompson@...aro.org>,
	Bruno Herrera <bruherrera@...il.com>,
	Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH v2 2/9] drivers: irqchip: Add STM32 external interrupts support

Hi Linus,

Sorry for the late reply, I was off last week.

2016-04-08 11:38 GMT+02:00 Linus Walleij <linus.walleij@...aro.org>:
> On Thu, Mar 31, 2016 at 5:09 PM, Maxime Coquelin
> <mcoquelin.stm32@...il.com> wrote:
>
>> +static void stm32_irq_handler(struct irq_desc *desc)
>> +{
>> +       struct irq_domain *domain = irq_desc_get_handler_data(desc);
>> +       struct irq_chip_generic *gc = domain->gc->gc[0];
>> +       struct irq_chip *chip = irq_desc_get_chip(desc);
>> +       unsigned long pending;
>> +       int n;
>> +
>> +       chained_irq_enter(chip, desc);
>> +
>> +       pending = irq_reg_readl(gc, EXTI_PR);
>> +       for_each_set_bit(n, &pending, BITS_PER_LONG) {
>> +               generic_handle_irq(irq_find_mapping(domain, n));
>> +       }
>> +
>> +       chained_irq_exit(chip, desc);
>> +}
>
> Is this one of those cases where you should re-read the status register
> on every iteration, so as to avoid exiting and immediately re-entering
> the irq handler?
>
> C.g irq-vic.c:
>
> static int handle_one_vic(struct vic_device *vic, struct pt_regs *regs)
> {
>         u32 stat, irq;
>         int handled = 0;
>
>         while ((stat = readl_relaxed(vic->base + VIC_IRQ_STATUS))) {
>                 irq = ffs(stat) - 1;
>                 handle_domain_irq(vic->domain, irq, regs);
>                 handled = 1;
>         }
>
>         return handled;
> }

Indeed, it would be better doing it like this.
Do you think I could even do this with two nested loops to reduce the
number of reg accesses?
It would look like this (just compiled, not tested):

static void stm32_irq_handler(struct irq_desc *desc)
{
    struct irq_domain *domain = irq_desc_get_handler_data(desc);
    struct irq_chip_generic *gc = domain->gc->gc[0];
    struct irq_chip *chip = irq_desc_get_chip(desc);
    unsigned long pending;
    int n;

    chained_irq_enter(chip, desc);

    while ((pending = irq_reg_readl(gc, EXTI_PR))) {
        for_each_set_bit(n, &pending, BITS_PER_LONG) {
            generic_handle_irq(irq_find_mapping(domain, n));
        }
    }

    chained_irq_exit(chip, desc);
}

Thanks,
Maxime