PCI: Add pci_irq_type() to query the allocated interrupt typegrafted

Add a helper that returns PCI_IRQ_MSIX, PCI_IRQ_MSI, or PCI_IRQ_INTX
based on the interrupt type the PCI core selected after
pci_alloc_irq_vectors().

Several drivers already open-code this check against pdev->msix_enabled
and pdev->msi_enabled, or even open code this helper [1].

A common helper avoids the duplication and keeps drivers from accessing
the bitfield directly (see also [2]).

Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: John Hubbard <jhubbard@nvidia.com>
Link: https://elixir.bootlin.com/linux/v7.1/source/drivers/net/ethernet/aquantia/atlantic/aq_pci_func.c#L196 [1]
Inspired-by: John Hubbard <jhubbard@nvidia.com>
Link: https://lore.kernel.org/all/DKKG2QM3YJYB.Z2H2B2UXJ75N@kernel.org/ [2]
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260813165234.620555-5-dakr@kernel.org
[ Add missing pci_irq_type() stub for CONFIG_PCI=n. ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-driver-pciback b/Documentation/ABI/testing/sysfs-driver-pciback
new file mode 100644
index 000000000..49f5fd0c8
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-driver-pciback
@@ -0,0 +1,28 @@
+What:           /sys/bus/pci/drivers/pciback/quirks
+Date:           Oct 2011
+KernelVersion:  3.1
+Contact:        xen-devel@lists.xenproject.org
+Description:
+                If the permissive attribute is set, then writing a string in
+                the format of DDDD:BB:DD.F-REG:SIZE:MASK will allow the guest
+                to write and read from the PCI device. That is Domain:Bus:
+                Device.Function-Register:Size:Mask (Domain is optional).
+                For example::
+
+                  #echo 00:19.0-E0:2:FF > /sys/bus/pci/drivers/pciback/quirks
+
+                will allow the guest to read and write to the configuration
+                register 0x0E.
+
+What:           /sys/bus/pci/drivers/pciback/allow_interrupt_control
+Date:           Jan 2020
+KernelVersion:  5.6
+Contact:        xen-devel@lists.xenproject.org
+Description:
+                List of devices which can have interrupt control flag (INTx,
+                MSI, MSI-X) set by a connected guest. It is meant to be set
+                only when the guest is a stubdomain hosting device model (qemu)
+                and the actual device is assigned to a HVM. It is not safe
+                (similar to permissive attribute) to set for a devices assigned
+                to a PV guest. The device is automatically removed from this
+                list when the connected pcifront terminates.