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, 55 insertions, 0 deletions

diff --git a/Documentation/i2c/old-module-parameters.rst b/Documentation/i2c/old-module-parameters.rst
new file mode 100644
index 000000000..b08b6daab
--- /dev/null
+++ b/Documentation/i2c/old-module-parameters.rst
@@ -0,0 +1,55 @@
+================================================================
+I2C device driver binding control from user-space in old kernels
+================================================================
+
+.. NOTE::
+   Note: this section is only relevant if you are handling some old code
+   found in kernel 2.6. If you work with more recent kernels, you can
+   safely skip this section.
+
+Up to kernel 2.6.32, many I2C drivers used helper macros provided by
+<linux/i2c.h> which created standard module parameters to let the user
+control how the driver would probe I2C buses and attach to devices. These
+parameters were known as ``probe`` (to let the driver probe for an extra
+address), ``force`` (to forcibly attach the driver to a given device) and
+``ignore`` (to prevent a driver from probing a given address).
+
+With the conversion of the I2C subsystem to the standard device driver
+binding model, it became clear that these per-module parameters were no
+longer needed, and that a centralized implementation was possible. The new,
+sysfs-based interface is described in
+Documentation/i2c/instantiating-devices.rst, section
+"Method 4: Instantiate from user-space".
+
+Below is a mapping from the old module parameters to the new interface.
+
+Attaching a driver to an I2C device
+-----------------------------------
+
+Old method (module parameters)::
+
+  # modprobe <driver> probe=1,0x2d
+  # modprobe <driver> force=1,0x2d
+  # modprobe <driver> force_<device>=1,0x2d
+
+New method (sysfs interface)::
+
+  # echo <device> 0x2d > /sys/bus/i2c/devices/i2c-1/new_device
+
+Preventing a driver from attaching to an I2C device
+---------------------------------------------------
+
+Old method (module parameters)::
+
+  # modprobe <driver> ignore=1,0x2f
+
+New method (sysfs interface)::
+
+  # echo dummy 0x2f > /sys/bus/i2c/devices/i2c-1/new_device
+  # modprobe <driver>
+
+Of course, it is important to instantiate the ``dummy`` device before loading
+the driver. The dummy device will be handled by i2c-core itself, preventing
+other drivers from binding to it later on. If there is a real device at the
+problematic address, and you want another driver to bind to it, then simply
+pass the name of the device in question instead of ``dummy``.