PCI/MSI: Reject multi-MSI early

When hierarchical MSI interrupt domains are enabled then there is no point
to do tons of work and detect the missing support for multi-MSI late in the
allocation path.

Just query the domain feature flags right away. The query function is going
to be used for other purposes later and has a mode argument which influences
the result:

  ALLOW_LEGACY returns true when:
     - there is no irq domain attached (legacy support)
     - there is a irq domain attached which has the feature flag set

  DENY_LEGACY returns only true when:
     - there is a irq domain attached which has the feature flag set

This allows to use the function universally without ifdeffery in the
calling code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20221111122015.574339988@linutronix.de

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/pci/msi/msi.h b/drivers/pci/msi/msi.h
index 8170ef2c5ad0..9d75b6fb3e0c 100644
--- a/drivers/pci/msi/msi.h
+++ b/drivers/pci/msi/msi.h
@@ -97,6 +97,15 @@ int __pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries, int
 void __pci_restore_msi_state(struct pci_dev *dev);
 void __pci_restore_msix_state(struct pci_dev *dev);
 
+/* irq_domain related functionality */
+
+enum support_mode {
+	ALLOW_LEGACY,
+	DENY_LEGACY,
+};
+
+bool pci_msi_domain_supports(struct pci_dev *dev, unsigned int feature_mask, enum support_mode mode);
+
 /* Legacy (!IRQDOMAIN) fallbacks */
 
 #ifdef CONFIG_PCI_MSI_ARCH_FALLBACKS