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, 95 insertions, 0 deletions

diff --git a/Documentation/networking/netif-msg.rst b/Documentation/networking/netif-msg.rst
new file mode 100644
index 000000000..b20d265a7
--- /dev/null
+++ b/Documentation/networking/netif-msg.rst
@@ -0,0 +1,95 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+NETIF Msg Level
+===============
+
+The design of the network interface message level setting.
+
+History
+-------
+
+ The design of the debugging message interface was guided and
+ constrained by backwards compatibility previous practice.  It is useful
+ to understand the history and evolution in order to understand current
+ practice and relate it to older driver source code.
+
+ From the beginning of Linux, each network device driver has had a local
+ integer variable that controls the debug message level.  The message
+ level ranged from 0 to 7, and monotonically increased in verbosity.
+
+ The message level was not precisely defined past level 3, but were
+ always implemented within +-1 of the specified level.  Drivers tended
+ to shed the more verbose level messages as they matured.
+
+   - 0  Minimal messages, only essential information on fatal errors.
+   - 1  Standard messages, initialization status.  No run-time messages
+   - 2  Special media selection messages, generally timer-driver.
+   - 3  Interface starts and stops, including normal status messages
+   - 4  Tx and Rx frame error messages, and abnormal driver operation
+   - 5  Tx packet queue information, interrupt events.
+   - 6  Status on each completed Tx packet and received Rx packets
+   - 7  Initial contents of Tx and Rx packets
+
+ Initially this message level variable was uniquely named in each driver
+ e.g. "lance_debug", so that a kernel symbolic debugger could locate and
+ modify the setting.  When kernel modules became common, the variables
+ were consistently renamed to "debug" and allowed to be set as a module
+ parameter.
+
+ This approach worked well.  However there is always a demand for
+ additional features.  Over the years the following emerged as
+ reasonable and easily implemented enhancements
+
+   - Using an ioctl() call to modify the level.
+   - Per-interface rather than per-driver message level setting.
+   - More selective control over the type of messages emitted.
+
+ The netif_msg recommendation adds these features with only a minor
+ complexity and code size increase.
+
+ The recommendation is the following points
+
+  - Retaining the per-driver integer variable "debug" as a module
+    parameter with a default level of '1'.
+
+  - Adding a per-interface private variable named "msg_enable".  The
+    variable is a bit map rather than a level, and is initialized as::
+
+       1 << debug
+
+    Or more precisely::
+
+	debug < 0 ? 0 : 1 << min(sizeof(int)-1, debug)
+
+    Messages should changes from::
+
+      if (debug > 1)
+	   printk(MSG_DEBUG "%s: ...
+
+    to::
+
+      if (np->msg_enable & NETIF_MSG_LINK)
+	   printk(MSG_DEBUG "%s: ...
+
+
+The set of message levels is named
+
+
+  =========   ===================	============
+  Old level   Name			Bit position
+  =========   ===================	============
+    0         NETIF_MSG_DRV		0x0001
+    1         NETIF_MSG_PROBE		0x0002
+    2         NETIF_MSG_LINK		0x0004
+    2         NETIF_MSG_TIMER		0x0004
+    3         NETIF_MSG_IFDOWN		0x0008
+    3         NETIF_MSG_IFUP		0x0008
+    4         NETIF_MSG_RX_ERR		0x0010
+    4         NETIF_MSG_TX_ERR		0x0010
+    5         NETIF_MSG_TX_QUEUED	0x0020
+    5         NETIF_MSG_INTR		0x0020
+    6         NETIF_MSG_TX_DONE		0x0040
+    6         NETIF_MSG_RX_STATUS	0x0040
+    7         NETIF_MSG_PKTDATA		0x0080
+  =========   ===================	============