[PATCH net-next 1/9] doc: net: add backplane documentation

[Florinel Iordache]

Add ethernet backplane documentation

Signed-off-by: Florinel Iordache <florinel.iordache@xxxxxxx>
---
 Documentation/networking/backplane.rst | 165 +++++++++++++++++++++++++++++++++
 1 file changed, 165 insertions(+)
 create mode 100644 Documentation/networking/backplane.rst

diff --git a/Documentation/networking/backplane.rst b/Documentation/networking/backplane.rst
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+.. SPDX-License-Identifier: (GPL-2.0+ OR BSD-3-Clause)
+
+=========================
+Ethernet Backplane Driver
+=========================
+
+Author:
+Florinel Iordache <florinel.iordache@xxxxxxx>
+
+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
-- 
1.9.1