genirq/MSI: Relax msi_domain_alloc() to support parentless MSI irqdomains

Previously msi_domain_alloc() assumed MSI irqdomains always had parent
irqdomains, but that's not true for the new Intel VMD devices.  Relax
msi_domain_alloc() to support parentless MSI irqdomains.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 5 insertions, 3 deletions

diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index 6b0c0b74a2a1..5e15cb4b2f00 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -109,9 +109,11 @@ static int msi_domain_alloc(struct irq_domain *domain, unsigned int virq,
         if (irq_find_mapping(domain, hwirq) > 0)
                 return -EEXIST;
 
-        ret = irq_domain_alloc_irqs_parent(domain, virq, nr_irqs, arg);
-        if (ret < 0)
-                return ret;
+        if (domain->parent) {
+                ret = irq_domain_alloc_irqs_parent(domain, virq, nr_irqs, arg);
+                if (ret < 0)
+                        return ret;
+        }
 
         for (i = 0; i < nr_irqs; i++) {
                 ret = ops->msi_init(domain, info, virq + i, hwirq + i, arg);