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Subject[PATCH 1/3] PCI/MSI: Initial hook for archs to declare multivector MSI support
For the most part multivector MSI is not supported and drivers and
hardware wanting multiple vectors opt for MSI-X instead. It seems
though that having the ability to query the arch/platform code to
determine whether allocating multiple MSI vectors will ever succeed
is a useful thing. For instance, vfio-pci can use this to determine
whether to expose multiple MSI vectors to the user. If we know we
cannot ever support more than one vector, we have a better shot at
the userspace driver working, especially if it's a guest OS, if we
only expose one vector as being available in the interface.

Signed-off-by: Alex Williamson <>

drivers/pci/msi.c | 5 +++++
include/linux/msi.h | 1 +
2 files changed, 6 insertions(+)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 9fab30a..36b503a 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -79,6 +79,11 @@ int __weak arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
return 0;

+bool __weak arch_supports_multivector_msi(struct pci_dev *dev)
+ return false;
* We have a default implementation available as a separate non-weak
* function, as it is used by the Xen x86 PCI code
diff --git a/include/linux/msi.h b/include/linux/msi.h
index 44f4746..2365c64 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -58,6 +58,7 @@ void arch_teardown_msi_irq(unsigned int irq);
int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type);
void arch_teardown_msi_irqs(struct pci_dev *dev);
void arch_restore_msi_irqs(struct pci_dev *dev);
+bool arch_supports_multivector_msi(struct pci_dev *dev);

void default_teardown_msi_irqs(struct pci_dev *dev);
void default_restore_msi_irqs(struct pci_dev *dev);

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