Add ethernet backplane documentation
Signed-off-by: Florinel Iordache <florinel.iordache@xxxxxxx>
---
Documentation/networking/backplane.rst | 159 +++++++++++++++++++++++++++++++++
Documentation/networking/phy.rst | 9 +-
2 files changed, 165 insertions(+), 3 deletions(-)
create mode 100644 Documentation/networking/backplane.rst
diff --git a/Documentation/networking/backplane.rst b/Documentation/networking/backplane.rst
new file mode 100644
index 0000000..fb91ba8
--- /dev/null
+++ b/Documentation/networking/backplane.rst
@@ -0,0 +1,159 @@
+.. 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
+
+Supported platforms
+===================
+
+Ethernet Backplane is enabled on the following platforms:
+
+LS1046A
diff --git a/Documentation/networking/phy.rst b/Documentation/networking/phy.rst
index 2561060..ec17c31 100644
--- a/Documentation/networking/phy.rst
+++ b/Documentation/networking/phy.rst
@@ -279,9 +279,12 @@ 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.
--
1.9.1
