Re: [Qemu-devel] [Android-virt] [PATCH] arm: make sure that number of irqs can be represented in GICD_TYPER.

[Christoffer Dall]

On Sun, Feb 19, 2012 at 6:07 PM, Rusty Russell <address@hidden> wrote:
> We currently assume that the number of interrupts (ITLinesNumber in
> the architecture reference manual) is divisible by 32, since we
> present it to the guest when it reads GICD_TYPER (in gic_dist_readb())
> as (N - 32) / 1.
>
> Signed-off-by: Rusty Russell <address@hidden>
>
> diff --git a/hw/arm_gic.c b/hw/arm_gic.c
> index fa6a60a..6446800 100644
> --- a/hw/arm_gic.c
> +++ b/hw/arm_gic.c
> @@ -818,6 +818,15 @@ static void gic_init(gic_state *s, int num_irq)
>         hw_error("requested %u interrupt lines exceeds GIC maximum %d\n",
>                  num_irq, GIC_MAXIRQ);
>     }
> +    /* ITLinesNumber is represented as (N - 32) / 1 (see
> +     * gic_dist_readb) so this is an implementation imposed
> +     * restriction, not an architectural one:
> +     */

What is this division by 1? Isn't (N - 32) / 1 == (N - 32) and how
does that explain the division. Was it (N / 32) - 1? Or is this a
cast? Or am I missing something completely?

> +    if (s->num_irq < 32 || (s->num_irq % 32)) {
> +        hw_error("%d interrupt lines unsupported: not divisible by 32\n",
> +                 num_irq);
> +    }
> +
>     qdev_init_gpio_in(&s->busdev.qdev, gic_set_irq, s->num_irq - 
> GIC_INTERNAL);
>     for (i = 0; i < NUM_CPU(s); i++) {
>         sysbus_init_irq(&s->busdev, &s->parent_irq[i]);
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