[PATCH v3 13/14] PCI/MSI: Document the various ways of ending up with NO_MSI

Marc Zyngier
2021-03-30T15:24:47Z

We have now three ways of ending up with NO_MSI being set.
Document them.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
drivers/pci/msi.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index d9c73c173c14..217dc9f0231f 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -871,8 +871,15 @@ static int pci_msi_supported(struct pci_dev *dev, int nvec)
* Any bridge which does NOT route MSI transactions from its
* secondary bus to its primary bus must set NO_MSI flag on
* the secondary pci_bus.
- * We expect only arch-specific PCI host bus controller driver
- * or quirks for specific PCI bridges to be setting NO_MSI.
+ *
+ * The NO_MSI flag can either be set directly by:
+ * - arch-specific PCI host bus controller drivers (deprecated)
+ * - quirks for specific PCI bridges
+ *
+ * or indirectly by platform-specific PCI host bridge drivers by
+ * advertising the 'msi_domain' property, which results in
+ * the NO_MSI flag when no MSI domain is found for this bridge
+ * at probe time.
*/
for (bus = dev->bus; bus; bus = bus->parent)
if (bus->bus_flags & PCI_BUS_FLAGS_NO_MSI)
--
2.29.2