Re: [PATCH v2 08/34] misc: xlink-pcie: Add documentation for XLink PCIe driver

[Randy Dunlap <rdunlap@infradead.org>]

Hi,
Here are a few doc comments for you:

On 1/8/21 1:25 PM, mgross@linux.intel.com wrote:
> From: Srikanth Thokala <srikanth.thokala@intel.com>
> 
> Provide overview of XLink PCIe driver implementation
> 
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: linux-doc@vger.kernel.org
> Reviewed-by: Mark Gross <mgross@linux.intel.com>
> Signed-off-by: Srikanth Thokala <srikanth.thokala@intel.com>
> ---
>  Documentation/vpu/index.rst      |  1 +
>  Documentation/vpu/xlink-pcie.rst | 90 ++++++++++++++++++++++++++++++++
>  2 files changed, 91 insertions(+)
>  create mode 100644 Documentation/vpu/xlink-pcie.rst
> 

> diff --git a/Documentation/vpu/xlink-pcie.rst b/Documentation/vpu/xlink-pcie.rst
> new file mode 100644
> index 000000000000..2d877c966b1e
> --- /dev/null
> +++ b/Documentation/vpu/xlink-pcie.rst
> @@ -0,0 +1,90 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +================================
> +Kernel driver: Xlink-pcie driver
> +================================
> +Supported chips:
> +  * Intel Edge.AI Computer Vision platforms: Keem Bay
> +    Suffix: Bay
> +    Slave address: 6240
> +    Datasheet: Publicly available at Intel
> +
> +Author: Srikanth Thokala Srikanth.Thokala@intel.com
> +
> +Introduction
> +============
> +The Xlink-pcie driver provides transport layer implementation for
> +the data transfers to support Xlink protocol subsystem communication with the
> +peer device. i.e, between remote host system and Keem Bay device.

        device, i.e.,

> +
> +The Keem Bay device is an ARM-based SOC that includes a vision processing
> +unit (VPU) and deep learning, neural network core in the hardware.
> +The Xlink-pcie driver exports a functional device endpoint to the Keem Bay
> +device and supports two-way communication with the peer device.
> +
> +High-level architecture
> +=======================
> +Remote Host: IA CPU
> +Local Host: ARM CPU (Keem Bay)::
> +
> +        +------------------------------------------------------------------------+
> +        |  Remote Host IA CPU              | | Local Host ARM CPU (Keem Bay) |   |
> +        +==================================+=+===============================+===+
> +        |  User App                        | | User App                      |   |
> +        +----------------------------------+-+-------------------------------+---+
> +        |   XLink UAPI                     | | XLink UAPI                    |   |
> +        +----------------------------------+-+-------------------------------+---+
> +        |   XLink Core                     | | XLink Core                    |   |
> +        +----------------------------------+-+-------------------------------+---+
> +        |   XLink PCIe                     | | XLink PCIe                    |   |
> +        +----------------------------------+-+-------------------------------+---+
> +        |   XLink-PCIe Remote Host driver  | | XLink-PCIe Local Host driver  |   |
> +        +----------------------------------+-+-------------------------------+---+
> +        |-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:|:|:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:|
> +        +----------------------------------+-+-------------------------------+---+
> +        |     PCIe Host Controller         | | PCIe Device Controller        | HW|
> +        +----------------------------------+-+-------------------------------+---+
> +               ^                                             ^
> +               |                                             |
> +               |------------- PCIe x2 Link  -----------------|
> +
> +This XLink PCIe driver comprises of two variants:
> +* Local Host driver
> +
> +  * Intended for ARM CPU
> +  * It is based on PCI Endpoint Framework
> +  * Driver path: {tree}/drivers/misc/Xlink-pcie/local_host
> +
> +* Remote Host driver
> +
> +       * Intended for IA CPU
> +       * It is a PCIe endpoint driver
> +       * Driver path: {tree}/drivers/misc/Xlink-pcie/remote_host
> +
> +XLink PCIe communication between local host and remote host is achieved through
> +ring buffer management and MSI/Doorbell interrupts.
> +
> +The Xlink-pcie driver subsystem registers the Keem Bay device as an endpoint
> +driver and provides standard linux PCIe sysfs interface, #

                                Linux
What is the '#' sign for above?

> +/sys/bus/pci/devices/xxxx:xx:xx.0/
> +
> +
> +XLink protocol subsystem
> +========================
> +Xlink is an abstracted control and communication subsystem based on channel
> +identification. It is intended to support VPU technology both at SoC level as
> +well as at IP level, over multiple interfaces.
> +
> +- The Xlink subsystem abstracts several types of communication channels
> +  underneath, allowing the usage of different interfaces with the
> +  same function call interface.
> +- The Communication channels are full-duplex protocol channels allowing
> +  concurrent bidirectional communication.
> +- The Xlink subsystem also supports control operations to VPU either
> +  from standalone local system or from remote system based on communication
> +  interface underneath.
> +- The Xlink subsystem supports the following communication interfaces:
> +    * USB CDC
> +    * Gigabit Ethernet
> +    * PCIe
> +    * IPC
> 


-- 
~Randy
"He closes his eyes and drops the goggles.  You can't get hurt
by looking at a bitmap.  Or can you?"
(Neal Stephenson: Snow Crash)