From 61af69296cbadf4c88a1076a3b3e5572827b04c8 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Tue, 30 Mar 2021 16:11:44 +0100 Subject: [PATCH] PCI/MSI: Document the various ways of ending up with NO_MSI We have now three ways of ending up with NO_MSI being set. Document them. Link: https://lore.kernel.org/r/20210330151145.997953-14-maz@kernel.org Signed-off-by: Marc Zyngier Signed-off-by: Lorenzo Pieralisi Acked-by: Bjorn Helgaas --- 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)