linux/drivers/xen
Konrad Rzeszutek Wilk 3a69e9165a xen: Find an unbound irq number in reverse order (high to low).
In earlier Xen Linux kernels, the IRQ mapping was a straight 1:1 and the
find_unbound_irq started looking around 256 for open IRQs and up. IRQs
from 0 to 255 were reserved for PCI devices.  Previous to this patch,
the 'find_unbound_irq'  started looking at get_nr_hw_irqs() number.
For privileged  domain where the ACPI information is available that
returns the upper-bound of what the GSIs. For non-privileged PV domains,
where ACPI is no-existent the get_nr_hw_irqs() reports the IRQ_LEGACY (16).
With PCI passthrough enabled, and with PCI cards that have IRQs pinned
to a higher number than 16 we collide with previously allocated IRQs.
Specifically the PCI IRQs collide with the IPI's for Xen functions
(as they are allocated earlier).
For example:

00:00.11 USB Controller: ATI Technologies Inc SB700 USB OHCI1 Controller (prog-if 10 [OHCI])
	...
	Interrupt: pin A routed to IRQ 18

[root@localhost ~]# cat /proc/interrupts | head
           CPU0       CPU1       CPU2
 16:      38186          0          0   xen-dyn-virq      timer0
 17:        149          0          0   xen-dyn-ipi       spinlock0
 18:        962          0          0   xen-dyn-ipi       resched0

and when the USB controller is loaded, the kernel reports:
IRQ handler type mismatch for IRQ 18
current handler: resched0

One way to fix this is to reverse the logic when looking for un-used
IRQ numbers and start with the highest available number. With that,
we would get:

           CPU0       CPU1       CPU2
... snip ..
292:         35          0          0   xen-dyn-ipi       callfunc0
293:       3992          0          0   xen-dyn-ipi       resched0
294:        224          0          0   xen-dyn-ipi       spinlock0
295:      57183          0          0   xen-dyn-virq      timer0
NMI:          0          0          0   Non-maskable interrupts
.. snip ..

And interrupts for PCI cards are now accessible.

This patch also includes the fix, found by Ian Campbell, titled
"xen: fix off-by-one error in find_unbound_irq."

[v2: Added an explanation in the code]
[v3: Rebased on top of tip/irq/core]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
2010-10-18 10:49:10 -04:00
..
xenbus Merge branch 'for-2.6.36' of git://git.kernel.dk/linux-2.6-block 2010-08-10 15:22:42 -07:00
xenfs Merge branch 'xen/xenbus' into upstream/xen 2010-08-04 14:49:24 -07:00
balloon.c xen: Rename the balloon lock 2010-06-07 14:34:07 -04:00
biomerge.c xen: define BIOVEC_PHYS_MERGEABLE() 2010-10-18 10:40:28 -04:00
cpu_hotplug.c Merge branch 'linux-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jbarnes/pci-2.6 2009-12-11 12:18:16 -08:00
events.c xen: Find an unbound irq number in reverse order (high to low). 2010-10-18 10:49:10 -04:00
evtchn.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
features.c xen: clean up asm/xen/hypervisor.h 2008-12-16 21:50:31 +01:00
grant-table.c xen: Xen PCI platform device driver. 2010-07-22 16:46:09 -07:00
Kconfig Merge branch 'stable/xen-swiotlb-0.8.6' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen 2010-08-12 09:09:41 -07:00
Makefile xen: define BIOVEC_PHYS_MERGEABLE() 2010-10-18 10:40:28 -04:00
manage.c Input: sysrq - drop tty argument form handle_sysrq() 2010-08-21 00:34:45 -07:00
platform-pci.c x86: Unplug emulated disks and nics. 2010-07-26 23:13:25 -07:00
swiotlb-xen.c swiotlb-xen: SWIOTLB library for Xen PV guest with PCI passthrough. 2010-07-27 11:51:00 -04:00
sys-hypervisor.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
xencomm.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00