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, 83 insertions, 0 deletions

diff --git a/Documentation/driver-api/usb/bulk-streams.rst b/Documentation/driver-api/usb/bulk-streams.rst
new file mode 100644
index 000000000..eeefe582f
--- /dev/null
+++ b/Documentation/driver-api/usb/bulk-streams.rst
@@ -0,0 +1,83 @@
+USB bulk streams
+~~~~~~~~~~~~~~~~
+
+Background
+==========
+
+Bulk endpoint streams were added in the USB 3.0 specification.  Streams allow a
+device driver to overload a bulk endpoint so that multiple transfers can be
+queued at once.
+
+Streams are defined in sections 4.4.6.4 and 8.12.1.4 of the Universal Serial Bus
+3.0 specification at https://www.usb.org/developers/docs/  The USB Attached SCSI
+Protocol, which uses streams to queue multiple SCSI commands, can be found on
+the T10 website (https://t10.org/).
+
+
+Device-side implications
+========================
+
+Once a buffer has been queued to a stream ring, the device is notified (through
+an out-of-band mechanism on another endpoint) that data is ready for that stream
+ID.  The device then tells the host which "stream" it wants to start.  The host
+can also initiate a transfer on a stream without the device asking, but the
+device can refuse that transfer.  Devices can switch between streams at any
+time.
+
+
+Driver implications
+===================
+
+::
+
+  int usb_alloc_streams(struct usb_interface *interface,
+		struct usb_host_endpoint **eps, unsigned int num_eps,
+		unsigned int num_streams, gfp_t mem_flags);
+
+Device drivers will call this API to request that the host controller driver
+allocate memory so the driver can use up to num_streams stream IDs.  They must
+pass an array of usb_host_endpoints that need to be setup with similar stream
+IDs.  This is to ensure that a UASP driver will be able to use the same stream
+ID for the bulk IN and OUT endpoints used in a Bi-directional command sequence.
+
+The return value is an error condition (if one of the endpoints doesn't support
+streams, or the xHCI driver ran out of memory), or the number of streams the
+host controller allocated for this endpoint.  The xHCI host controller hardware
+declares how many stream IDs it can support, and each bulk endpoint on a
+SuperSpeed device will say how many stream IDs it can handle.  Therefore,
+drivers should be able to deal with being allocated less stream IDs than they
+requested.
+
+Do NOT call this function if you have URBs enqueued for any of the endpoints
+passed in as arguments.  Do not call this function to request less than two
+streams.
+
+Drivers will only be allowed to call this API once for the same endpoint
+without calling usb_free_streams().  This is a simplification for the xHCI host
+controller driver, and may change in the future.
+
+
+Picking new Stream IDs to use
+=============================
+
+Stream ID 0 is reserved, and should not be used to communicate with devices.  If
+usb_alloc_streams() returns with a value of N, you may use streams 1 though N.
+To queue an URB for a specific stream, set the urb->stream_id value.  If the
+endpoint does not support streams, an error will be returned.
+
+Note that new API to choose the next stream ID will have to be added if the xHCI
+driver supports secondary stream IDs.
+
+
+Clean up
+========
+
+If a driver wishes to stop using streams to communicate with the device, it
+should call::
+
+  void usb_free_streams(struct usb_interface *interface,
+		struct usb_host_endpoint **eps, unsigned int num_eps,
+		gfp_t mem_flags);
+
+All stream IDs will be deallocated when the driver releases the interface, to
+ensure that drivers that don't support streams will be able to use the endpoint.