Hi Linus,

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

2016-04-08 11:38 GMT+02:00 Linus Walleij [off-list ref]:

On Thu, Mar 31, 2016 at 5:09 PM, Maxime Coquelin
[off-list ref] wrote:

quoted

+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