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PCI/MSI: Document the various ways of ending up with NO_MSI

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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 <maz@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
This commit is contained in:
Marc Zyngier 2021-03-30 16:11:44 +01:00 committed by Lorenzo Pieralisi
parent 645e9c3838
commit 61af69296c
1 changed files with 9 additions and 2 deletions
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11
drivers/pci/msi.c
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@ -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)