diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 733b32fda3903ffa93199fcc88af52b2c8622779..46b9441b36bdc8d92332f5d309920e94b7742861 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -1129,31 +1129,69 @@ static int its_alloc_device_irq(struct its_device *dev, irq_hw_number_t *hwirq)
 	return 0;
 }
 
+struct its_pci_alias {
+	struct pci_dev	*pdev;
+	u32		dev_id;
+	u32		count;
+};
+
+static int its_pci_msi_vec_count(struct pci_dev *pdev)
+{
+	int msi, msix;
+
+	msi = max(pci_msi_vec_count(pdev), 0);
+	msix = max(pci_msix_vec_count(pdev), 0);
+
+	return max(msi, msix);
+}
+
+static int its_get_pci_alias(struct pci_dev *pdev, u16 alias, void *data)
+{
+	struct its_pci_alias *dev_alias = data;
+
+	dev_alias->dev_id = alias;
+	if (pdev != dev_alias->pdev)
+		dev_alias->count += its_pci_msi_vec_count(dev_alias->pdev);
+
+	return 0;
+}
+
 static int its_msi_prepare(struct irq_domain *domain, struct device *dev,
 			   int nvec, msi_alloc_info_t *info)
 {
 	struct pci_dev *pdev;
 	struct its_node *its;
-	u32 dev_id;
 	struct its_device *its_dev;
+	struct its_pci_alias dev_alias;
 
 	if (!dev_is_pci(dev))
 		return -EINVAL;
 
 	pdev = to_pci_dev(dev);
-	dev_id = PCI_DEVID(pdev->bus->number, pdev->devfn);
+	dev_alias.pdev = pdev;
+	dev_alias.count = nvec;
+
+	pci_for_each_dma_alias(pdev, its_get_pci_alias, &dev_alias);
 	its = domain->parent->host_data;
 
-	its_dev = its_find_device(its, dev_id);
-	if (WARN_ON(its_dev))
-		return -EINVAL;
+	its_dev = its_find_device(its, dev_alias.dev_id);
+	if (its_dev) {
+		/*
+		 * We already have seen this ID, probably through
+		 * another alias (PCI bridge of some sort). No need to
+		 * create the device.
+		 */
+		dev_dbg(dev, "Reusing ITT for devID %x\n", dev_alias.dev_id);
+		goto out;
+	}
 
-	its_dev = its_create_device(its, dev_id, nvec);
+	its_dev = its_create_device(its, dev_alias.dev_id, dev_alias.count);
 	if (!its_dev)
 		return -ENOMEM;
 
-	dev_dbg(&pdev->dev, "ITT %d entries, %d bits\n", nvec, ilog2(nvec));
-
+	dev_dbg(&pdev->dev, "ITT %d entries, %d bits\n",
+		dev_alias.count, ilog2(dev_alias.count));
+out:
 	info->scratchpad[0].ptr = its_dev;
 	info->scratchpad[1].ptr = dev;
 	return 0;