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Date:   Fri, 24 Apr 2020 15:46:23 +0300
From:   Florinel Iordache <florinel.iordache@....com>
To:     davem@...emloft.net, netdev@...r.kernel.org, andrew@...n.ch,
        f.fainelli@...il.com, hkallweit1@...il.com, linux@...linux.org.uk
Cc:     devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
        robh+dt@...nel.org, mark.rutland@....com, kuba@...nel.org,
        corbet@....net, shawnguo@...nel.org, leoyang.li@....com,
        madalin.bucur@....nxp.com, ioana.ciornei@....com,
        linux-kernel@...r.kernel.org,
        Florinel Iordache <florinel.iordache@....com>
Subject: [PATCH net-next v2 1/9] doc: net: add backplane documentation

Add ethernet backplane documentation

Signed-off-by: Florinel Iordache <florinel.iordache@....com>
---
 Documentation/ABI/testing/sysfs-class-net-phydev |   2 +-
 Documentation/networking/backplane.rst           | 165 +++++++++++++++++++++++
 Documentation/networking/phy.rst                 |  15 ++-
 3 files changed, 178 insertions(+), 4 deletions(-)
 create mode 100644 Documentation/networking/backplane.rst

diff --git a/Documentation/ABI/testing/sysfs-class-net-phydev b/Documentation/ABI/testing/sysfs-class-net-phydev
index 206cbf5..69dbd36 100644
--- a/Documentation/ABI/testing/sysfs-class-net-phydev
+++ b/Documentation/ABI/testing/sysfs-class-net-phydev
@@ -39,7 +39,7 @@ Description:
 		<empty> (not available), mii, gmii, sgmii, tbi, rev-mii,
 		rmii, rgmii, rgmii-id, rgmii-rxid, rgmii-txid, rtbi, smii
 		xgmii, moca, qsgmii, trgmii, 1000base-x, 2500base-x, rxaui,
-		xaui, 10gbase-kr, unknown
+		xaui, 10gbase-kr, 40gbase-kr4, unknown
 
 What:		/sys/class/mdio_bus/<bus>/<device>/phy_standalone
 Date:		May 2019
diff --git a/Documentation/networking/backplane.rst b/Documentation/networking/backplane.rst
new file mode 100644
index 0000000..951c17e
--- /dev/null
+++ b/Documentation/networking/backplane.rst
@@ -0,0 +1,165 @@
+.. SPDX-License-Identifier: (GPL-2.0+ OR BSD-3-Clause)
+
+=========================
+Ethernet Backplane Driver
+=========================
+
+Author:
+Florinel Iordache <florinel.iordache@....com>
+
+Contents
+========
+
+	- Ethernet Backplane Overview
+	- Equalization
+	- Auto-negotiation
+	- Link training
+	- Enable backplane support in Linux kernel
+	- Ethernet Backplane support architecture
+	- Supported equalization algorithms
+	- Supported backplane protocols
+	- Supported platforms
+
+Ethernet Backplane Overview
+===========================
+
+Ethernet operation over electrical backplanes, also referred to as Ethernet
+Backplane, combines the IEEE 802.3 Media Access Control (MAC) and MAC
+Control sublayers with a family of Physical Layers defined to support
+operation over a modular chassis backplane.
+The main standard specification for Ethernet Backplane is: IEEE802.3ap-2007
+Amendment 4: Ethernet Operation over Electrical Backplanes
+which includes the new Clause 69 through Clause 74.
+Additional specifications define support for various speeds and 4-lanes:
+IEEE802.3ba-2010.
+Signal equalization is required based on the link quality. The standard
+specifies that a start-up algorithm should be in place in order to get the
+link up.
+
+Equalization
+============
+
+Equalization represents the procedure required to minimize the effects of signal
+distortion, noise, interference occurred in high-speed communication channels.
+The equalizer purpose is to improve signal integrity in terms of bit error rate
+(BER) in order to allow accurate recovery of the transmitted symbols.
+
+A simplified view of channel equalization:
+
+            LD       <======== channel =========>      LP
+       Local Device                                Link Partner
+
+         |-----|                                         ___
+         |     |     <======== channel =========>       /   |
+         |     |      witout signal Equalization       /     \
+         |     |                                      /      |
+     ____|     |____                              ___/        \___
+
+         |\   _                                        |-----|
+         | \_/ |     <======== channel =========>      |     |
+         |     |       with signal Equalization        |     |
+         |     |                                       |     |
+     ____|     |____                               ____|     |____
+
+      LD Tx waveform                                LP Rx waveform
+
+Auto-negotiation
+================
+
+Auto-negotiation allows the devices at both ends of a link segment to advertise
+abilities, acknowledge receipt, and discover the common modes of operation that
+both devices share. It also rejects the use of operational modes not shared by
+both devices. Auto-negotiation does not test link segment characteristics.
+
+Link training
+=============
+
+Link training occurs after auto-negotiation has determined the link to be a
+Base-KR, but before auto-negotiation is done. It continuously exchanges messages
+(training frames) between the local and the remote device as part of the
+start-up phase. Link training tunes the equalization parameters of the remote and
+local transmitter to improve the link quality in terms of bit error rate.
+Both LP (link partner/remote device) and LD (local device) perform link training
+in parallel. Link training is finished when both sides decide that the channel is
+equalized and then the link is considered up.
+
+Enable backplane support in Linux kernel
+========================================
+
+To enable the Ethernet Backplane, the following Kconfig options are available:
+
+# enable generic Ethernet Backplane support:
+CONFIG_ETH_BACKPLANE=y
+# enable Fixed (No Equalization) algorithm:
+CONFIG_ETH_BACKPLANE_FIXED=y
+# enable 3-Taps Bit Edge Equalization (BEE) algorithm:
+CONFIG_ETH_BACKPLANE_BEE=y
+# enable QorIQ Ethernet Backplane driver:
+CONFIG_ETH_BACKPLANE_QORIQ=y
+
+Ethernet Backplane support architecture
+=======================================
+
+Ethernet Backplane support in Linux kernel complies with the following standard
+design concepts:
+* Modularity:
+    # internal components are separated in well defined functional modules
+* Reusability:
+    # lower layer components provide basic functionalities which are reused by
+    the upper layer modules
+* Extensibility:
+    # architecture can be easily extended with support for new:
+    	- backplane protocols
+    	- equalization algorithms
+    	- supported devices
+It is designed as a loosely coupled architecture in order to allow the
+possibility to easily create desired backplane system configurations according
+to user needs by specifying different components and initialization parameters
+without recompiling the kernel.
+
+       ------------------            ------------------------------------
+       |  EQ Algorithms |            |    Specific device drivers       |
+       |  ------------  |            |       Backplane support          |
+       |  |  Fixed   |  |            | ------------------   ----------- |
+       |  ------------  |            | |     QorIQ      |   |         | |
+       |  |   BEE    |  |            | |    devices     |   |         | |
+       |  ------------  |            | | -------------- |   |  other  | |
+       |  |  others  |  |            | | | Serdes 10G | |   | devices | |
+  ----------------------------       | | -------------- |   | support | |
+  |      Link Training       |       | | | Serdes 28G | |   |         | |
+  |   and Auto-negotiation   |       | | -------------- |   |         | |
+  |    (IEEE 802.3-ap/ba)    |       | |----------------|   |---------| |
+  ---------------------------------------------------------------------------
+  |                   Ethernet Backplane Generic Driver                     |
+  ---------------------------------------------------------------------------
+  |                         PHY Abstraction Layer                           |
+  ---------------------------------------------------------------------------
+
+Supported equalization algorithms
+=================================
+
+Ethernet Backplane supports the following equalization algorithms:
+
+- Fixed setup (No Equalization algorithm)
+- 3-Taps Bit Edge Equalization (BEE) algorithm
+
+Supported backplane protocols
+=============================
+
+Ethernet Backplane supports the following protocols:
+
+- Single-lane:
+10GBase-KR
+
+- Multi-lane:
+40GBase-KR4
+
+Supported platforms
+===================
+
+Ethernet Backplane is enabled on the following platforms:
+
+LS1046A
+LS1088A
+LS2088A
+LX2160A
\ No newline at end of file
diff --git a/Documentation/networking/phy.rst b/Documentation/networking/phy.rst
index 2561060..1f1ebf2 100644
--- a/Documentation/networking/phy.rst
+++ b/Documentation/networking/phy.rst
@@ -279,13 +279,22 @@ Some of the interface modes are described below:
     XFI and SFI are not PHY interface types in their own right.
 
 ``PHY_INTERFACE_MODE_10GKR``
-    This is the IEEE 802.3 Clause 49 defined 10GBASE-R with Clause 73
-    autonegotiation. Please refer to the IEEE standard for further
-    information.
+    This is 10G Ethernet Backplane over single lane specified in
+    IEEE802.3ap-2007 Amendment 4: Ethernet Operation over Electrical
+    Backplanes which includes the new Clause 69 through Clause 74
+    including autonegotiation. 10GKR uses the same physical layer
+    encoding as 10GBASE-R defined in IEEE802.3 Clause 49. Please refer
+    to the IEEE standard for further information.
 
     Note: due to legacy usage, some 10GBASE-R usage incorrectly makes
     use of this definition.
 
+``PHY_INTERFACE_MODE_40GKR4``
+    This is 40G Ethernet Backplane over 4-lanes using the same main
+    standard used for Ethernet Operation over Electrical Backplanes
+    and additional specifications that define support for Ethernet
+    Backplane over 4-lanes specified in IEEE802.3ba-2010.
+
 Pause frames / flow control
 ===========================
 
-- 
1.9.1

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