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    SubjectRe: [PATCH 1/2] ARM: gic: add irq_domain support
    On Wed, Sep 28, 2011 at 10:53:55PM -0500, Rob Herring wrote:
    > From: Rob Herring <rob.herring@calxeda.com>
    >
    > Convert the gic interrupt controller to use irq domains in preparation
    > for device-tree binding and MULTI_IRQ. This allows for translation between
    > GIC interrupt IDs and Linux irq numbers.
    >
    > The meaning of irq_offset has changed. It now is just the number of skipped
    > GIC interrupt IDs for the controller. It will be 16 for primary GIC and 32
    > for secondary GICs.

    [...]

    > /*
    > @@ -81,7 +82,7 @@ static inline unsigned int gic_irq(struct irq_data *d)
    > */
    > static void gic_mask_irq(struct irq_data *d)
    > {
    > - u32 mask = 1 << (d->irq % 32);
    > + u32 mask = 1 << (gic_irq(d) % 32);

    This can probably change simply to d->hwirq if irq_offset is
    eliminated as I describe below.

    > void __init gic_init(unsigned int gic_nr, unsigned int irq_start,
    > void __iomem *dist_base, void __iomem *cpu_base)
    > {
    > struct gic_chip_data *gic;
    > + struct irq_domain *domain;
    > + int gic_irqs;
    >
    > BUG_ON(gic_nr >= MAX_GIC_NR);
    >
    > gic = &gic_data[gic_nr];
    > + domain = &gic->domain;
    > gic->dist_base = dist_base;
    > gic->cpu_base = cpu_base;
    > - gic->irq_offset = (irq_start - 1) & ~31;
    >
    > - if (gic_nr == 0)
    > + /*
    > + * For primary GICs, skip over SGIs.
    > + * For secondary GICs, skip over PPIs, too.
    > + */
    > + if (gic_nr == 0) {
    > gic_cpu_base_addr = cpu_base;
    > + gic->irq_offset = 16;
    > + irq_start = (irq_start & ~31) + 16;

    With the switch to irq_domain, there should no longer be any need for
    a ~31 mask on the irq_start number. Yes, you'll want to make sure
    that it doesn't allocate below irq 16, but the driver should
    completely use the irq_domain to manage the mapping from linux-irq
    number to hwirq number. The ~31 mask appears to have been an
    optimization to quickly calculate hwirq number from the linux one, but
    that value is now found in irq_data->hwirq.

    irq_offset could almost be dropped entirely outside of probe because
    it no longer matters. Instead, populate the to_irq() hook so that the
    hwirq value gets set correctly from the outset.

    It would be better in general to have a consistent view of what the
    hwirq number means regardless of if it is a root GIC.

    g.


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