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Message-ID: <2adb27fe-1b2e-3488-eedf-46b01ee25ace@infradead.org>
Date: Thu, 28 Jan 2021 17:05:41 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Kishon Vijay Abraham I <kishon@...com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Jonathan Corbet <corbet@....net>,
Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
Arnd Bergmann <arnd@...db.de>, Jon Mason <jdmason@...zu.us>,
Dave Jiang <dave.jiang@...el.com>,
Allen Hubbe <allenbh@...il.com>,
Tom Joseph <tjoseph@...ence.com>, Rob Herring <robh@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-pci@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-ntb@...glegroups.com
Subject: Re: [PATCH v9 01/17] Documentation: PCI: Add specification for the
*PCI NTB* function device
On 1/4/21 7:28 AM, Kishon Vijay Abraham I wrote:
> Add specification for the *PCI NTB* function device. The endpoint function
> driver and the host PCI driver should be created based on this
> specification.
>
> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
> ---
> Documentation/PCI/endpoint/index.rst | 1 +
> .../PCI/endpoint/pci-ntb-function.rst | 351 ++++++++++++++++++
> 2 files changed, 352 insertions(+)
> create mode 100644 Documentation/PCI/endpoint/pci-ntb-function.rst
> diff --git a/Documentation/PCI/endpoint/pci-ntb-function.rst b/Documentation/PCI/endpoint/pci-ntb-function.rst
> new file mode 100644
> index 000000000000..a57908be4047
> --- /dev/null
> +++ b/Documentation/PCI/endpoint/pci-ntb-function.rst
> @@ -0,0 +1,351 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=================
> +PCI NTB Function
> +=================
> +
> +:Author: Kishon Vijay Abraham I <kishon@...com>
> +
> +PCI Non Transparent Bridges (NTB) allow two host systems to communicate
preferably
Non-Transparent
> +with each other by exposing each host as a device to the other host.
> +NTBs typically support the ability to generate interrupts on the remote
> +machine, expose memory ranges as BARs and perform DMA. They also support
> +scratchpads which are areas of memory within the NTB that are accessible
> +from both machines.
> +
> +PCI NTB Function allows two different systems (or hosts) to communicate
> +with each other by configurig the endpoint instances in such a way that
> +transactions from one system is routed to the other system.
> +
> +In the below diagram, PCI NTB function configures the SoC with multiple
> +PCIe Endpoint (EP) instances in such a way that transaction from one EP
> +controller is routed to the other EP controller. Once PCI NTB function
> +configures the SoC with multiple EP instances, HOST1 and HOST2 can
> +communicate with each other using SoC as a bridge.
> +
> +.. code-block:: text
> +
> + +-------------+ +-------------+
> + | | | |
> + | HOST1 | | HOST2 |
> + | | | |
> + +------^------+ +------^------+
> + | |
> + | |
> + +---------|-------------------------------------------------|---------+
> + | +------v------+ +------v------+ |
> + | | | | | |
> + | | EP | | EP | |
> + | | CONTROLLER1 | | CONTROLLER2 | |
> + | | <-----------------------------------> | |
> + | | | | | |
> + | | | | | |
> + | | | SoC With Multiple EP Instances | | |
> + | | | (Configured using NTB Function) | | |
> + | +-------------+ +-------------+ |
> + +---------------------------------------------------------------------+
> +
> +Constructs used for Implementing NTB
> +====================================
> +
> + 1) Config Region
> + 2) Self Scratchpad Registers
> + 3) Peer Scratchpad Registers
> + 4) Doorbell Registers
> + 5) Memory Window
> +
> +
> +Config Region:
> +--------------
> +
> +Config Region is a construct that is specific to NTB implemented using NTB
> +Endpoint Function Driver. The host and endpoint side NTB function driver will
> +exchange information with each other using this region. Config Region has
> +Control/Status Registers for configuring the Endpoint Controller. Host can
> +write into this region for configuring the outbound ATU and to indicate the
what is ATU?
> +link status. Endpoint can indicate the status of commands issued be host in
by ??
> +this region. Endpoint can also indicate the scratchpad offset, number of
> +memory windows to the host using this region.
> +
> +The format of Config Region is given below. Each of the fields here are 32
Each is
> +bits.
> +
> +.. code-block:: text
> +
> + +------------------------+
> + | COMMAND |
> + +------------------------+
> + | ARGUMENT |
> + +------------------------+
> + | STATUS |
> + +------------------------+
> + | TOPOLOGY |
> + +------------------------+
> + | ADDRESS (LOWER 32) |
> + +------------------------+
> + | ADDRESS (UPPER 32) |
> + +------------------------+
> + | SIZE |
> + +------------------------+
> + | NO OF MEMORY WINDOW |
> + +------------------------+
> + | MEMORY WINDOW1 OFFSET |
> + +------------------------+
> + | SPAD OFFSET |
> + +------------------------+
> + | SPAD COUNT |
> + +------------------------+
> + | DB ENTRY SIZE |
> + +------------------------+
> + | DB DATA |
> + +------------------------+
> + | : |
> + +------------------------+
> + | : |
> + +------------------------+
> + | DB DATA |
> + +------------------------+
> +
> +
> + COMMAND:
> +
> + NTB function supports three commands:
> +
> + CMD_CONFIGURE_DOORBELL (0x1): Command to configure doorbell. Before
> + invoking this command, the host should allocate and initialize
> + MSI/MSI-X vectors (i.e initialize the MSI/MSI-X capability in the
i.e.
> + Endpoint). The endpoint on receiving this command will configure
> + the outbound ATU such that transaction to DB BAR will be routed
> + to the MSI/MSI-X address programmed by the host. The ARGUMENT
> + register should be populated with number of DBs to configure (in the
> + lower 16 bits) and if MSI or MSI-X should be configured (BIT 16).
> + (TODO: Add support for MSI-X).
> +
> + CMD_CONFIGURE_MW (0x2): Command to configure memory window. The
> + host invokes this command after allocating a buffer that can be
> + accessed by remote host. The allocated address should be programmed
> + in the ADDRESS register (64 bit), the size should be programmed in
> + the SIZE register and the memory window index should be programmed
> + in the ARGUMENT register. The endpoint on receiving this command
> + will configure the outbound ATU such that trasaction to MW BAR
transaction
> + will be routed to the address provided by the host.
> +
> + CMD_LINK_UP (0x3): Command to indicate an NTB application is
> + bound to the EP device on the host side. Once the endpoint
> + receives this command from both the hosts, the endpoint will
> + raise an LINK_UP event to both the hosts to indicate the hosts
> + can start communicating with each other.
> +
> + ARGUMENT:
> +
> + The value of this register is based on the commands issued in
> + command register. See COMMAND section for more information.
> +
> + TOPOLOGY:
> +
> + Set to NTB_TOPO_B2B_USD for Primary interface
> + Set to NTB_TOPO_B2B_DSD for Secondary interface
> +
> + ADDRESS/SIZE:
> +
> + Address and Size to be used while configuring the memory window.
> + See "CMD_CONFIGURE_MW" for more info.
> +
> + MEMORY WINDOW1 OFFSET:
> +
> + Memory Window 1 and Doorbell registers are packed together in the
> + same BAR. The initial portion of the region will have doorbell
> + registers and the latter portion of the region is for memory window 1.
> + This register will specify the offset of the memory window 1.
> +
> + NO OF MEMORY WINDOW:
> +
> + Specifies the number of memory windows supported by the NTB device.
> +
> + SPAD OFFSET:
> +
> + Self scratchpad region and config region are packed together in the
> + same BAR. The initial portion of the region will have config region
> + and the latter portion of the region is for self scratchpad. This
> + register will specify the offset of the self scratchpad registers.
> +
> + SPAD COUNT:
> +
> + Specifies the number of scratchpad registers supported by the NTB
> + device.
> +
> + DB ENTRY SIZE:
> +
> + Used to determine the offset within the DB BAR that should be written
> + in order to raise doorbell. EPF NTB can use either MSI/MSI-X to
> + ring doorbell (MSI-X support will be added later). MSI uses same
> + address for all the interrupts and MSI-X can provide different
> + addresses for different interrupts. The MSI/MSI-X address is provided
> + by the host and the address it gives is based on the MSI/MSI-X
> + implementation supported by the host. For instance, ARM platform
> + using GIC ITS will have same MSI-X address for all the interrupts.
> + In order to support all the combinations and use the same mechanism
> + for both MSI and MSI-X, EPF NTB allocates separate region in the
> + Outbound Address Space for each of the interrupts. This region will
> + be mapped to the MSI/MSI-X address provided by the host. If a host
> + provides the same address for all the interrupts, all the regions
> + will be translated to the same address. If a host provides different
> + address, the regions will be translated to different address. This
> + will ensure there is no difference while raising the doorbell.
> +
> + DB DATA:
> +
> + EPF NTB supports 32 interrupts. So there are 32 DB DATA registers.
> + This holds the MSI/MSI-X data that has to be written to MSI address
> + for raising doorbell interrupt. This will be populated by EPF NTB
> + while invoking CMD_CONFIGURE_DOORBELL.
> +
> +Scratchpad Registers:
> +---------------------
> +
> + Each host has it's own register space allocated in the memory of NTB EPC.
its
[it's means "it is"]
> + They are both readable and writable from both sides of the bridge. They
> + are used by applications built over NTB and can be used to pass control
> + and status information between both sides of a device.
> +
> + Scratchpad registers has 2 parts
> + 1) Self Scratchpad: Host's own register space
> + 2) Peer Scratchpad: Remote host's register space.
> +
> +Doorbell Registers:
> +-------------------
> +
> + Registers using which one host can interrupt the other host.
eh? ENOPARSE.
> +
> +Memory Window:
> +--------------
> +
> + Actual transfer of data between the two hosts will happen using the
> + memory window.
> +
> +Modeling Constructs:
> +====================
> +
> +There are 5 or more distinct regions (config, self scratchpad, peer
> +scratchpad, doorbell, one or more memory windows) to be modeled to achieve
> +NTB functionality. Atleast one memory window is required while more than
At least
> +one is permitted. All these regions should be mapped to BAR for hosts to
> +access these regions.
> +
> +If one 32-bit BAR is allocated for each of these regions, the scheme would
> +look like
> +
> +====== ===============
> +BAR NO CONSTRUCTS USED
> +====== ===============
> +BAR0 Config Region
> +BAR1 Self Scratchpad
> +BAR2 Peer Scratchpad
> +BAR3 Doorbell
> +BAR4 Memory Window 1
> +BAR5 Memory Window 2
> +====== ===============
> +
> +However if we allocate a separate BAR for each of the region, there would not
regions,
> +be enough BARs for all the regions in a platform that supports only 64-bit
> +BAR.
> +
> +In order to be supported by most of the platforms, the regions should be
> +packed and mapped to BARs in a way that provides NTB functionality and
> +also making sure the hosts doesn't access any region that it is not supposed
> +to.
> +
> +The following scheme is used in EPF NTB Function
> +
> +====== ===============================
> +BAR NO CONSTRUCTS USED
> +====== ===============================
> +BAR0 Config Region + Self Scratchpad
> +BAR1 Peer Scratchpad
> +BAR2 Doorbell + Memory Window 1
> +BAR3 Memory Window 2
> +BAR4 Memory Window 3
> +BAR5 Memory Window 4
> +====== ===============================
> +
> +With this scheme, for the basic NTB functionality 3 BARs should be sufficient.
> +
> +Modeling Config/Scratchpad Region:
> +----------------------------------
> +
> +.. code-block:: text
> +
> + +-----------------+------->+------------------+ +-----------------+
> + | BAR0 | | CONFIG REGION | | BAR0 |
> + +-----------------+----+ +------------------+<-------+-----------------+
> + | BAR1 | | |SCRATCHPAD REGION | | BAR1 |
> + +-----------------+ +-->+------------------+<-------+-----------------+
> + | BAR2 | Local Memory | BAR2 |
> + +-----------------+ +-----------------+
> + | BAR3 | | BAR3 |
> + +-----------------+ +-----------------+
> + | BAR4 | | BAR4 |
> + +-----------------+ +-----------------+
> + | BAR5 | | BAR5 |
> + +-----------------+ +-----------------+
> + EP CONTROLLER 1 EP CONTROLLER 2
> +
> +Above diagram shows Config region + Scratchpad region for HOST1 (connected to
> +EP controller 1) allocated in local memory. The HOST1 can access the config
> +region and scratchpad region (self scratchpad) using BAR0 of EP controller 1.
> +The peer host (HOST2 connected to EP controller 2) can also access this
> +scratchpad region (peer scratchpad) using BAR1 of EP controller 2. This
> +diagram shows the case where Config region and Scratchpad region is allocated
> +for HOST1, however the same is applicable for HOST2.
> +
> +Modeling Doorbell/Memory Window 1:
> +----------------------------------
> +
> +.. code-block:: text
> +
> + +-----------------+ +----->+----------------+-----------+-----------------+
> + | BAR0 | | | Doorbell 1 +-----------> MSI-X ADDRESS 1 |
> + +-----------------+ | +----------------+ +-----------------+
> + | BAR1 | | | Doorbell 2 +---------+ | |
> + +-----------------+----+ +----------------+ | | |
> + | BAR2 | | Doorbell 3 +-------+ | +-----------------+
> + +-----------------+----+ +----------------+ | +-> MSI-X ADDRESS 2 |
> + | BAR3 | | | Doorbell 4 +-----+ | +-----------------+
> + +-----------------+ | |----------------+ | | | |
> + | BAR4 | | | | | | +-----------------+
> + +-----------------+ | | MW1 +---+ | +-->+ MSI-X ADDRESS 3||
> + | BAR5 | | | | | | +-----------------+
> + +-----------------+ +----->-----------------+ | | | |
> + EP CONTROLLER 1 | | | | +-----------------+
> + | | | +---->+ MSI-X ADDRESS 4 |
> + +----------------+ | +-----------------+
> + EP CONTROLLER 2 | | |
> + (OB SPACE) | | |
> + +-------> MW1 |
> + | |
> + | |
> + +-----------------+
> + | |
> + | |
> + | |
> + | |
> + | |
> + +-----------------+
> + PCI Address Space
> + (Managed by HOST2)
> +
> +Above diagram shows how the doorbell and memory window 1 is mapped so that
> +HOST1 can raise doorbell interrupt on HOST2 and also how HOST1 can access
> +buffers exposed by HOST2 using memory window1 (MW1). Here doorbell and
> +memory window 1 regions are allocated in EP controller 2 outbound (OB) address
> +space. Allocating and configuring BARs for doorbell and memory window1
> +is done during the initialization phase of NTB endpoint function driver.
> +Mapping from EP controller 2 OB space to PCI address space is done when HOST2
> +sends CMD_CONFIGURE_MW/CMD_CONFIGURE_DOORBELL. The commands are explained
> +below.
below??
> +
> +Modeling Optional Memory Windows:
> +---------------------------------
> +
> +This is modeled the same was as MW1 but each of the additional memory windows
> +is mapped to separate BARs.
>
Is all of this register/memory space mapping defined in some PCI NTB spec
or is this specific to some hardware/SoC implementation?
HTH.
--
~Randy
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