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

From: Jonathan Cameron <[email-masked]>
Date: Fri, 7 Jun 2024 18:43:31 +0100

On Fri, 31 May 2024 16:38:39 -0500
Wei Huang <[email-masked]> wrote:

> Provide a document for TPH feature, including the description of
> kernel options and driver API interface.
> 
> Co-developed-by: Eric Van Tassell <[email-masked]>
> Signed-off-by: Eric Van Tassell <[email-masked]>
> Signed-off-by: Wei Huang <[email-masked]>
> Reviewed-by: Ajit Khaparde <[email-masked]>
> Reviewed-by: Somnath Kotur <[email-masked]> 
> Reviewed-by: Andy Gospodarek <[email-masked]>
Sort and sweet.

Reviewed-by: Jonathan Cameron <[email-masked]>

> ---
>  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 <[email-masked]>
> +          - Wei Huang <[email-masked]>
> +
> +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
>  ---------------------------
>