[PATCH V2 7/9] PCI/TPH: Add TPH documentation

Wei Huang
2024-05-31T21:40:44Z

Provide a document for TPH feature, including the description of
kernel options and driver API interface.

Co-developed-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
---
Documentation/PCI/index.rst | 1 +
Documentation/PCI/tph.rst | 57 ++++++++++++++++++++++++++++
Documentation/driver-api/pci/pci.rst | 3 ++
3 files changed, 61 insertions(+)
create mode 100644 Documentation/PCI/tph.rst

diff --git a/Documentation/PCI/index.rst b/Documentation/PCI/index.rst
index e73f84aebde3..5e7c4e6e726b 100644
--- a/Documentation/PCI/index.rst
+++ b/Documentation/PCI/index.rst
@@ -18,3 +18,4 @@ PCI Bus Subsystem
pcieaer-howto
endpoint/index
boot-interrupts
+ tph
diff --git a/Documentation/PCI/tph.rst b/Documentation/PCI/tph.rst
new file mode 100644
index 000000000000..ea9c8313f3e4
--- /dev/null
+++ b/Documentation/PCI/tph.rst
@@ -0,0 +1,57 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========
+TPH Support
+===========
+
+
+:Copyright: 2024 Advanced Micro Devices, Inc.
+:Authors: - Eric van Tassell <eric.vantassell@amd.com>
+ - Wei Huang <wei.huang2@amd.com>
+
+Overview
+========
+TPH (TLP Processing Hints) is a PCIe feature that allows endpoint devices
+to provide optimization hints, such as desired caching behavior, for
+requests that target memory space. These hints, in a format called steering
+tags, are provided in the requester's TLP headers and can empower the system
+hardware, including the Root Complex, to optimize the utilization of platform
+resources for the requests.
+
+User Guide
+==========
+
+Kernel Options
+--------------
+There are two kernel command line options available to control TPH feature
+
+ * "notph": TPH will be disabled for all endpoint devices.
+ * "nostmode": TPH will be enabled but the ST Mode will be forced to "No ST Mode".
+
+Device Driver API
+-----------------
+In brief, an endpoint device driver using the TPH interface to configure
+Interrupt Vector Mode will call pcie_tph_set_st() when setting up MSI-X
+interrupts as shown below:
+
+.. code-block:: c
+
+ for (i = 0, j = 0; i < nr_rings; i++) {
+ ...
+ rc = request_irq(irq->vector, irq->handler, flags, irq->name, NULL);
+ ...
+ if (!pcie_tph_set_st(pdev, i, cpumask_first(irq->cpu_mask),
+ TPH_MEM_TYPE_VM, PCI_TPH_REQ_TPH_ONLY))
+ pr_err("Error in configuring steering tag\n");
+ ...
+ }
+
+If a device only supports TPH vendor specific mode, its driver can call
+pcie_tph_get_st() to retrieve the steering tag for a specific CPU and uses
+the tag to control TPH behavior.
+
+.. kernel-doc:: drivers/pci/pcie/tph.c
+ :export:
+
+.. kernel-doc:: drivers/pci/pcie/tph.c
+ :identifiers: pcie_tph_set_st
diff --git a/Documentation/driver-api/pci/pci.rst b/Documentation/driver-api/pci/pci.rst
index aa40b1cc243b..3d896b2cf16e 100644
--- a/Documentation/driver-api/pci/pci.rst
+++ b/Documentation/driver-api/pci/pci.rst
@@ -46,6 +46,9 @@ PCI Support Library
.. kernel-doc:: drivers/pci/pci-sysfs.c
:internal:

+.. kernel-doc:: drivers/pci/pcie/tph.c
+ :export:
+
PCI Hotplug Support Library
---------------------------

--
2.44.0