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>

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index fb04fc8..aa6fba3 100644 (file)
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -925,6 +925,8 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
        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));

diff --git a/include/linux/pci.h b/include/linux/pci.h
index ebf557e..ede0aef 100644 (file)
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -550,6 +550,7 @@ 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,