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

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Date:	Fri, 8 Apr 2016 11:38:40 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Maxime Coquelin <mcoquelin.stm32@...il.com>
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

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;
}

Yours,
Linus Walleij