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author | Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> | 2010-12-09 14:53:29 -0500 |
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committer | Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> | 2010-12-09 16:02:35 -0500 |
commit | d1b758ebc2a82d738092cb42e742470f9d0ea53e (patch) | |
tree | 97002d5036d186b0900a8ad6a043a4f63492200f | |
parent | cf7d7e5a1980d1116ee152d25dac382b112b9c17 (diff) | |
download | linux-d1b758ebc2a82d738092cb42e742470f9d0ea53e.tar.gz linux-d1b758ebc2a82d738092cb42e742470f9d0ea53e.tar.bz2 linux-d1b758ebc2a82d738092cb42e742470f9d0ea53e.zip |
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: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
-rw-r--r-- | drivers/xen/events.c | 18 |
1 files changed, 12 insertions, 6 deletions
diff --git a/drivers/xen/events.c b/drivers/xen/events.c index 31af0ac31a98..4d4a23d4c9f6 100644 --- a/drivers/xen/events.c +++ b/drivers/xen/events.c @@ -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); |