PCI: endpoint: pci-ep-msi: Add checks for MSI parent and mutability

Some MSI controllers can change address/data pair during the execution of
irq_chip::irq_set_affinity() callback. Since the current PCI Endpoint
framework cannot support mutable MSI controllers, call
irq_domain_is_msi_immutable() API to check if the controller is immutable
or not.

Also ensure that the MSI domain is a parent MSI domain so that it can
allocate address/data pairs.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
[mani: reworded error message and commit message]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Niklas Cassel <cassel@kernel.org>
Link: https://patch.msgid.link/20250710-ep-msi-v21-4-57683fc7fb25@nxp.com

Author: nxpfrankli

drivers/pci/endpoint/pci-ep-msi.c

@@ -57,6 +57,14 @@ int pci_epf_alloc_doorbell(struct pci_epf *epf, u16 num_db)
 		return -ENODEV;
 	}
 
+	if (!irq_domain_is_msi_parent(domain))
+		return -ENODEV;
+
+	if (!irq_domain_is_msi_immutable(domain)) {
+		dev_err(dev, "Mutable MSI controller not supported\n");
+		return -ENODEV;
+	}
+
 	dev_set_msi_domain(epc->dev.parent, domain);
 
 	msg = kcalloc(num_db, sizeof(struct pci_epf_doorbell_msg), GFP_KERNEL);