xen: events: assume PHYSDEVOP_get_free_pirq exists

The find_unbound_pirq is called only from xen_allocate_pirq_msi and
only if alloc_pirq is true. The only caller which does this is
xen_hvm_setup_msi_irqs. The use of this function is gated, in
pci_xen_hvm_init, on XENFEAT_hvm_pirqs.

The PHYSDEVOP_get_free_pirq interfaces was added to the hypervisor in
22410:be96f6058c05 while XENFEAT_hvm_pirqs was added a couple of
minutes prior in 22409:6663214f06ac. Therefore we do not need to
concern ourselves with hypervisors which support XENFEAT_hvm_pirqs but
not PHYSDEVOP_get_free_pirq.

This eliminates the fallback path in find_unbound_pirq which walks to
pirq_to_irq array looking for a free pirq. Unlike the
PHYSDEVOP_get_free_pirq interface this fallback only looks up a free
pirq but does not reserve it. Removing this fallback will simplify
locking in the future.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 6 insertions, 9 deletions

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index ed3420df0937..c21066fc30be 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -649,19 +649,16 @@ out:
 
 static int find_unbound_pirq(int type)
 {
-        int rc, i;
+        int rc;
         struct physdev_get_free_pirq op_get_free_pirq;
-        op_get_free_pirq.type = type;
 
+        op_get_free_pirq.type = type;
         rc = HYPERVISOR_physdev_op(PHYSDEVOP_get_free_pirq, &op_get_free_pirq);
-        if (!rc)
-                return op_get_free_pirq.pirq;
 
-        for (i = 0; i < nr_irqs; i++) {
-                if (pirq_to_irq[i] < 0)
-                        return i;
-        }
-        return -1;
+        WARN_ONCE(rc == -ENOSYS,
+                  "hypervisor does not support the PHYSDEVOP_get_free_pirq interface\n");
+
+        return rc ? -1 : op_get_free_pirq.pirq;
 }
 
 int xen_allocate_pirq_msi(char *name, int *pirq, int alloc_pirq)