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    SubjectRe: [PATCH 1/5] xen: events: use irq_alloc_desc(_at) instead of open-coding an IRQ allocator.
     On 10/25/2010 10:35 AM, Konrad Rzeszutek Wilk wrote:
    > On Mon, Oct 25, 2010 at 05:23:29PM +0100, Ian Campbell wrote:
    >> Encapsulate allocate and free in xen_irq_alloc and xen_irq_free.
    >>
    >> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
    >> ---
    >> drivers/xen/events.c | 68 ++++++++++++++++++++-----------------------------
    >> 1 files changed, 28 insertions(+), 40 deletions(-)
    >>
    >> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
    >> index 97612f5..c8f3e43 100644
    >> --- a/drivers/xen/events.c
    >> +++ b/drivers/xen/events.c
    >> @@ -394,41 +394,29 @@ static int find_unbound_pirq(void)
    >> return -1;
    >> }
    >>
    >> -static int find_unbound_irq(void)
    >> +static int xen_irq_alloc(void)
    >> {
    >> - struct irq_data *data;
    >> - int irq, res;
    >> - int start = get_nr_hw_irqs();
    >> + int irq = irq_alloc_desc(0);
    >>
    >> - if (start == nr_irqs)
    >> - goto no_irqs;
    >> -
    >> - /* nr_irqs is a magic value. Must not use it.*/
    >> - for (irq = nr_irqs-1; irq > start; irq--) {
    >> - data = irq_get_irq_data(irq);
    >> - /* only 0->15 have init'd desc; handle irq > 16 */
    >> - if (!data)
    >> - break;
    >> - if (data->chip == &no_irq_chip)
    >> - break;
    >> - if (data->chip != &xen_dynamic_chip)
    >> - continue;
    >> - if (irq_info[irq].type == IRQT_UNBOUND)
    >> - return irq;
    >> - }
    >> -
    >> - if (irq == start)
    >> - goto no_irqs;
    >> + if (irq < 0)
    >> + panic("No available IRQ to bind to: increase nr_irqs!\n");
    >>
    >> - res = irq_alloc_desc_at(irq, 0);
    >> + return irq;
    >> +}
    > So I am curious what the /proc/interrupts looks?The issue (and the reason
    > for this implementation above) was that under PV with PCI devices we would
    > overlap PCI devices IRQs with Xen event channels. So we could have a USB device
    > at IRQ 16 _and_ also a xen_spinlock4 handler. That would throw off the system
    > since the xen_spinlock4 was an edge type handler while the USB device was an
    > level (at least on my box).

    What? Why? How? Surely if we're asking the irq subsystem to allocate
    us an irq, it will return a fresh never-before-used (and certainly not
    shared) irq? Shared irqs only make sense if multiple devices are
    actually sharing, say, a wire on the board.

    Or am I missing something?

    J



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