Documentation: net: octeontx2: Add RVU HW and drivers overview

Added high level overview of OcteonTx2 RVU HW and functionality of
various drivers which will be upstreamed.
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/device_drivers/index.rst

@@ -22,6 +22,7 @@ Contents:
    intel/iavf
    intel/ice
    google/gve
+   marvell/octeontx2
    mellanox/mlx5
    netronome/nfp
    pensando/ionic

Documentation/networking/device_drivers/marvell/octeontx2.rst

+.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+
+====================================
+Marvell OcteonTx2 RVU Kernel Drivers
+====================================
+
+Copyright (c) 2020 Marvell International Ltd.
+
+Contents
+========
+
+- `Overview`_
+- `Drivers`_
+- `Basic packet flow`_
+
+Overview
+========
+
+Resource virtualization unit (RVU) on Marvell's OcteonTX2 SOC maps HW
+resources from the network, crypto and other functional blocks into
+PCI-compatible physical and virtual functions. Each functional block
+again has multiple local functions (LFs) for provisioning to PCI devices.
+RVU supports multiple PCIe SRIOV physical functions (PFs) and virtual
+functions (VFs). PF0 is called the administrative / admin function (AF)
+and has privileges to provision RVU functional block's LFs to each of the
+PF/VF.
+
+RVU managed networking functional blocks
+ - Network pool or buffer allocator (NPA)
+ - Network interface controller (NIX)
+ - Network parser CAM (NPC)
+ - Schedule/Synchronize/Order unit (SSO)
+ - Loopback interface (LBK)
+
+RVU managed non-networking functional blocks
+ - Crypto accelerator (CPT)
+ - Scheduled timers unit (TIM)
+ - Schedule/Synchronize/Order unit (SSO)
+   Used for both networking and non networking usecases
+
+Resource provisioning examples
+ - A PF/VF with NIX-LF & NPA-LF resources works as a pure network device
+ - A PF/VF with CPT-LF resource works as a pure crypto offload device.
+
+RVU functional blocks are highly configurable as per software requirements.
+
+Firmware setups following stuff before kernel boots
+ - Enables required number of RVU PFs based on number of physical links.
+ - Number of VFs per PF are either static or configurable at compile time.
+   Based on config, firmware assigns VFs to each of the PFs.
+ - Also assigns MSIX vectors to each of PF and VFs.
+ - These are not changed after kernel boot.
+
+Drivers
+=======
+
+Linux kernel will have multiple drivers registering to different PF and VFs
+of RVU. Wrt networking there will be 3 flavours of drivers.
+
+Admin Function driver
+---------------------
+
+As mentioned above RVU PF0 is called the admin function (AF), this driver
+supports resource provisioning and configuration of functional blocks.
+Doesn't handle any I/O. It sets up few basic stuff but most of the
+funcionality is achieved via configuration requests from PFs and VFs.
+
+PF/VFs communicates with AF via a shared memory region (mailbox). Upon
+receiving requests AF does resource provisioning and other HW configuration.
+AF is always attached to host kernel, but PFs and their VFs may be used by host
+kernel itself, or attached to VMs or to userspace applications like
+DPDK etc. So AF has to handle provisioning/configuration requests sent
+by any device from any domain.
+
+AF driver also interacts with underlying firmware to
+ - Manage physical ethernet links ie CGX LMACs.
+ - Retrieve information like speed, duplex, autoneg etc
+ - Retrieve PHY EEPROM and stats.
+ - Configure FEC, PAM modes
+ - etc
+
+From pure networking side AF driver supports following functionality.
+ - Map a physical link to a RVU PF to which a netdev is registered.
+ - Attach NIX and NPA block LFs to RVU PF/VF which provide buffer pools, RQs, SQs
+   for regular networking functionality.
+ - Flow control (pause frames) enable/disable/config.
+ - HW PTP timestamping related config.
+ - NPC parser profile config, basically how to parse pkt and what info to extract.
+ - NPC extract profile config, what to extract from the pkt to match data in MCAM entries.
+ - Manage NPC MCAM entries, upon request can frame and install requested packet forwarding rules.
+ - Defines receive side scaling (RSS) algorithms.
+ - Defines segmentation offload algorithms (eg TSO)
+ - VLAN stripping, capture and insertion config.
+ - SSO and TIM blocks config which provide packet scheduling support.
+ - Debugfs support, to check current resource provising, current status of
+   NPA pools, NIX RQ, SQ and CQs, various stats etc which helps in debugging issues.
+ - And many more.
+
+Physical Function driver
+------------------------
+
+This RVU PF handles IO, is mapped to a physical ethernet link and this
+driver registers a netdev. This supports SR-IOV. As said above this driver
+communicates with AF with a mailbox. To retrieve information from physical
+links this driver talks to AF and AF gets that info from firmware and responds
+back ie cannot talk to firmware directly.
+
+Supports ethtool for configuring links, RSS, queue count, queue size,
+flow control, ntuple filters, dump PHY EEPROM, config FEC etc.
+
+Virtual Function driver
+-----------------------
+
+There are two types VFs, VFs that share the physical link with their parent
+SR-IOV PF and the VFs which work in pairs using internal HW loopback channels (LBK).
+
+Type1:
+ - These VFs and their parent PF share a physical link and used for outside communication.
+ - VFs cannot communicate with AF directly, they send mbox message to PF and PF
+   forwards that to AF. AF after processing, responds back to PF and PF forwards
+   the reply to VF.
+ - From functionality point of view there is no difference between PF and VF as same type
+   HW resources are attached to both. But user would be able to configure few stuff only
+   from PF as PF is treated as owner/admin of the link.
+
+Type2:
+ - RVU PF0 ie admin function creates these VFs and maps them to loopback block's channels.
+ - A set of two VFs (VF0 & VF1, VF2 & VF3 .. so on) works as a pair ie pkts sent out of
+   VF0 will be received by VF1 and viceversa.
+ - These VFs can be used by applications or virtual machines to communicate between them
+   without sending traffic outside. There is no switch present in HW, hence the support
+   for loopback VFs.
+ - These communicate directly with AF (PF0) via mbox.
+
+Except for the IO channels or links used for packet reception and transmission there is
+no other difference between these VF types. AF driver takes care of IO channel mapping,
+hence same VF driver works for both types of devices.
+
+Basic packet flow
+=================
+
+Ingress
+-------
+
+1. CGX LMAC receives packet.
+2. Forwards the packet to the NIX block.
+3. Then submitted to NPC block for parsing and then MCAM lookup to get the destination RVU device.
+4. NIX LF attached to the destination RVU device allocates a buffer from RQ mapped buffer pool of NPA block LF.
+5. RQ may be selected by RSS or by configuring MCAM rule with a RQ number.
+6. Packet is DMA'ed and driver is notified.
+
+Egress
+------
+
+1. Driver prepares a send descriptor and submits to SQ for transmission.
+2. The SQ is already configured (by AF) to transmit on a specific link/channel.
+3. The SQ descriptor ring is maintained in buffers allocated from SQ mapped pool of NPA block LF.
+4. NIX block transmits the pkt on the designated channel.
+5. NPC MCAM entries can be installed to divert pkt onto a different channel.

MAINTAINERS

@@ -10000,6 +10000,7 @@ M:	Jerin Jacob <jerinj@marvell.com>
 L:	netdev@vger.kernel.org
 S:	Supported
 F:	drivers/net/ethernet/marvell/octeontx2/af/
+F:	Documentation/networking/device_drivers/marvell/octeontx2.rst
 
 MATROX FRAMEBUFFER DRIVER
 L:	linux-fbdev@vger.kernel.org