From 94e89b145371b68fa0ea294855adebcd03e0522e Mon Sep 17 00:00:00 2001
From: Marc Zyngier <maz@kernel.org>
Date: Tue, 30 Mar 2021 16:11:41 +0100
Subject: PCI/MSI: Let PCI host bridges declare their reliance on MSI domains

There is a whole class of host bridges that cannot know whether
MSIs will be provided or not, as they rely on other blocks
to provide the MSI functionnality, using MSI domains.  This is
the case for example on systems that use the ARM GIC architecture.

Introduce a new attribute ('msi_domain') indicating that implicit
dependency, and use this property to set the NO_MSI flag when
no MSI domain is found at probe time.

Link: https://lore.kernel.org/r/20210330151145.997953-11-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/probe.c | 2 ++
 include/linux/pci.h | 1 +
 2 files changed, 3 insertions(+)

--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -925,6 +925,8 @@ static int pci_register_host_bridge(stru
 	device_enable_async_suspend(bus->bridge);
 	pci_set_bus_of_node(bus);
 	pci_set_bus_msi_domain(bus);
+	if (bridge->msi_domain && !dev_get_msi_domain(&bus->dev))
+		bus->bus_flags |= PCI_BUS_FLAGS_NO_MSI;
 
 	if (!parent)
 		set_dev_node(bus->bridge, pcibus_to_node(bus));
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -545,6 +545,7 @@ struct pci_host_bridge {
 	unsigned int	native_dpc:1;		/* OS may use PCIe DPC */
 	unsigned int	preserve_config:1;	/* Preserve FW resource setup */
 	unsigned int	size_windows:1;		/* Enable root bus sizing */
+	unsigned int	msi_domain:1;		/* Bridge wants MSI domain */
 
 	/* Resource alignment requirements */
 	resource_size_t (*align_resource)(struct pci_dev *dev,
