[PATCH v2 14/15] PCI/MSI: Document the various ways of ending up with NO_MSI
From: Marc Zyngier <maz@kernel.org>
Date: 2021-03-22 18:54:41
Also in:
linux-hyperv, linux-mediatek, linux-pci, linux-renesas-soc, linux-tegra, lkml
Subsystem:
pci subsystem, the rest · Maintainers:
Bjorn Helgaas, Linus Torvalds
We have now 4 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 | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index d9c73c173c14..425abcdfcaca 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c@@ -871,8 +871,16 @@ 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: + * - unconditionally advertising the 'no_msi' property + * - 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
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