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Commit d1b758eb authored by Konrad Rzeszutek Wilk's avatar Konrad Rzeszutek Wilk
Browse files

xen/irq: Cleanup the find_unbound_irq 



The "find_unbound_irq" is a bit unusual - it allocates
virtual IRQ (event channels) in reverse order. This means
starting at the "top" of the available IRQs (nr_irqs) down
to the GSI/MSI IRQs (nr_irqs_gsi). Lets document this and
also make the variables easier to understand.

Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent cf7d7e5a

drivers/xen/events.c

+12 −6
Original line number Diff line number Diff line
@@ -405,15 +405,21 @@ static int find_unbound_irq(void) 
{

	struct irq_data *data;

	int irq, res;

	int start = get_nr_hw_irqs();

	int bottom = get_nr_hw_irqs();

	int top = nr_irqs-1;



	if (start == nr_irqs)

	if (bottom == nr_irqs)

		goto no_irqs;



	/* nr_irqs is a magic value. Must not use it.*/

	for (irq = nr_irqs-1; irq > start; irq--) {

	/* This loop starts from the top of IRQ space and goes down.

	 * We need this b/c if we have a PCI device in a Xen PV guest

	 * we do not have an IO-APIC (though the backend might have them)

	 * mapped in. To not have a collision of physical IRQs with the Xen

	 * event channels start at the top of the IRQ space for virtual IRQs.

	 */

	for (irq = top; irq > bottom; irq--) {

		data = irq_get_irq_data(irq);

		/* only 0->15 have init'd desc; handle irq > 16 */

		/* only 15->0 have init'd desc; handle irq > 16 */

		if (!data)

			break;

		if (data->chip == &no_irq_chip)
@@ -424,7 +430,7 @@ static int find_unbound_irq(void) 
			return irq;

	}



	if (irq == start)

	if (irq == bottom)

		goto no_irqs;



	res = irq_alloc_desc_at(irq, -1);