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

["Thokala, Srikanth" <srikanth.thokala@intel.com>]

Hi Randy,

Thank you for the review.

> -----Original Message-----
> From: Randy Dunlap <rdunlap@infradead.org>
> Sent: Wednesday, January 20, 2021 1:06 AM
> To: mgross@linux.intel.com; markgross@kernel.org; arnd@arndb.de;
> bp@suse.de; damien.lemoal@wdc.com; dragan.cvetic@xilinx.com;
> gregkh@linuxfoundation.org; corbet@lwn.net; leonard.crestez@nxp.com;
> palmerdabbelt@google.com; paul.walmsley@sifive.com; peng.fan@nxp.com;
> robh+dt@kernel.org; shawnguo@kernel.org; jassisinghbrar@gmail.com
> Cc: linux-kernel@vger.kernel.org; Thokala, Srikanth
> <srikanth.thokala@intel.com>; linux-doc@vger.kernel.org
> Subject: Re: [PATCH v2 08/34] misc: xlink-pcie: Add documentation for
> XLink PCIe driver
> 
> 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.,

Ok.

> 
> > +
> > +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

Ok.

> What is the '#' sign for above?

It denotes Linux prompt; I will change it to be more meaningful.

Thanks!
Srikanth

> 
> > +/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)