edac.rst: move concepts dictionary from edac.h

Error Detection And Correction (EDAC) Devices

=============================================

Main Concepts used at the EDAC subsystem

----------------------------------------

There are several things to be aware of that aren't at all obvious, like

*sockets, *socket sets*, *banks*, *rows*, *chip-select rows*, *channels*,

etc...

These are some of the many terms that are thrown about that don't always

mean what people think they mean (Inconceivable!).  In the interest of

creating a common ground for discussion, terms and their definitions

will be established.

* Memory devices

The individual DRAM chips on a memory stick.  These devices commonly

output 4 and 8 bits each (x4, x8). Grouping several of these in parallel

provides the number of bits that the memory controller expects:

typically 72 bits, in order to provide 64 bits + 8 bits of ECC data.

* Memory Stick

A printed circuit board that aggregates multiple memory devices in

parallel.  In general, this is the Field Replaceable Unit (FRU) which

gets replaced, in the case of excessive errors. Most often it is also

called DIMM (Dual Inline Memory Module).

* Memory Socket

A physical connector on the motherboard that accepts a single memory

stick. Also called as "slot" on several datasheets.

* Channel

A memory controller channel, responsible to communicate with a group of

DIMMs. Each channel has its own independent control (command) and data

bus, and can be used independently or grouped with other channels.

* Branch

It is typically the highest hierarchy on a Fully-Buffered DIMM memory

controller. Typically, it contains two channels. Two channels at the

same branch can be used in single mode or in lockstep mode. When

lockstep is enabled, the cacheline is doubled, but it generally brings

some performance penalty. Also, it is generally not possible to point to

just one memory stick when an error occurs, as the error correction code

is calculated using two DIMMs instead of one. Due to that, it is capable

of correcting more errors than on single mode.

* Single-channel

The data accessed by the memory controller is contained into one dimm

only. E. g. if the data is 64 bits-wide, the data flows to the CPU using

one 64 bits parallel access. Typically used with SDR, DDR, DDR2 and DDR3

memories. FB-DIMM and RAMBUS use a different concept for channel, so

this concept doesn't apply there.

* Double-channel

The data size accessed by the memory controller is interlaced into two

dimms, accessed at the same time. E. g. if the DIMM is 64 bits-wide (72

bits with ECC), the data flows to the CPU using a 128 bits parallel

access.

* Chip-select row

This is the name of the DRAM signal used to select the DRAM ranks to be

accessed. Common chip-select rows for single channel are 64 bits, for

dual channel 128 bits. It may not be visible by the memory controller,

as some DIMM types have a memory buffer that can hide direct access to

it from the Memory Controller.

* Single-Ranked stick

A Single-ranked stick has 1 chip-select row of memory. Motherboards

commonly drive two chip-select pins to a memory stick. A single-ranked

stick, will occupy only one of those rows. The other will be unused.

.. _doubleranked:

* Double-Ranked stick

A double-ranked stick has two chip-select rows which access different

sets of memory devices.  The two rows cannot be accessed concurrently.

* Double-sided stick

**DEPRECATED TERM**, see :ref:`Double-Ranked stick <doubleranked>`.

A double-sided stick has two chip-select rows which access different sets

of memory devices. The two rows cannot be accessed concurrently.

"Double-sided" is irrespective of the memory devices being mounted on

both sides of the memory stick.

* Socket set

All of the memory sticks that are required for a single memory access or

all of the memory sticks spanned by a chip-select row.  A single socket

set has two chip-select rows and if double-sided sticks are used these

will occupy those chip-select rows.

* Bank

This term is avoided because it is unclear when needing to distinguish

between chip-select rows and socket sets.

Memory Controllers

------------------

#define OP_RUNNING_POLL_INTR	0x203

#define OP_OFFLINE		0x300

/*

 * Concepts used at the EDAC subsystem

 *

 * There are several things to be aware of that aren't at all obvious:

 *

 * SOCKETS, SOCKET SETS, BANKS, ROWS, CHIP-SELECT ROWS, CHANNELS, etc..

 *

 * These are some of the many terms that are thrown about that don't always

 * mean what people think they mean (Inconceivable!).  In the interest of

 * creating a common ground for discussion, terms and their definitions

 * will be established.

 *

 * Memory devices:	The individual DRAM chips on a memory stick.  These

 *			devices commonly output 4 and 8 bits each (x4, x8).

 *			Grouping several of these in parallel provides the

 *			number of bits that the memory controller expects:

 *			typically 72 bits, in order to provide 64 bits +

 *			8 bits of ECC data.

 *

 * Memory Stick:	A printed circuit board that aggregates multiple

 *			memory devices in parallel.  In general, this is the

 *			Field Replaceable Unit (FRU) which gets replaced, in

 *			the case of excessive errors. Most often it is also

 *			called DIMM (Dual Inline Memory Module).

 *

 * Memory Socket:	A physical connector on the motherboard that accepts

 *			a single memory stick. Also called as "slot" on several

 *			datasheets.

 *

 * Channel:		A memory controller channel, responsible to communicate

 *			with a group of DIMMs. Each channel has its own

 *			independent control (command) and data bus, and can

 *			be used independently or grouped with other channels.

 *

 * Branch:		It is typically the highest hierarchy on a

 *			Fully-Buffered DIMM memory controller.

 *			Typically, it contains two channels.

 *			Two channels at the same branch can be used in single

 *			mode or in lockstep mode.

 *			When lockstep is enabled, the cacheline is doubled,

 *			but it generally brings some performance penalty.

 *			Also, it is generally not possible to point to just one

 *			memory stick when an error occurs, as the error

 *			correction code is calculated using two DIMMs instead

 *			of one. Due to that, it is capable of correcting more

 *			errors than on single mode.

 *

 * Single-channel:	The data accessed by the memory controller is contained

 *			into one dimm only. E. g. if the data is 64 bits-wide,

 *			the data flows to the CPU using one 64 bits parallel

 *			access.

 *			Typically used with SDR, DDR, DDR2 and DDR3 memories.

 *			FB-DIMM and RAMBUS use a different concept for channel,

 *			so this concept doesn't apply there.

 *

 * Double-channel:	The data size accessed by the memory controller is

 *			interlaced into two dimms, accessed at the same time.

 *			E. g. if the DIMM is 64 bits-wide (72 bits with ECC),

 *			the data flows to the CPU using a 128 bits parallel

 *			access.

 *

 * Chip-select row:	This is the name of the DRAM signal used to select the

 *			DRAM ranks to be accessed. Common chip-select rows for

 *			single channel are 64 bits, for dual channel 128 bits.

 *			It may not be visible by the memory controller, as some

 *			DIMM types have a memory buffer that can hide direct

 *			access to it from the Memory Controller.

 *

 * Single-Ranked stick:	A Single-ranked stick has 1 chip-select row of memory.

 *			Motherboards commonly drive two chip-select pins to

 *			a memory stick. A single-ranked stick, will occupy

 *			only one of those rows. The other will be unused.

 *

 * Double-Ranked stick:	A double-ranked stick has two chip-select rows which

 *			access different sets of memory devices.  The two

 *			rows cannot be accessed concurrently.

 *

 * Double-sided stick:	DEPRECATED TERM, see Double-Ranked stick.

 *			A double-sided stick has two chip-select rows which

 *			access different sets of memory devices. The two

 *			rows cannot be accessed concurrently. "Double-sided"

 *			is irrespective of the memory devices being mounted

 *			on both sides of the memory stick.

 *

 * Socket set:		All of the memory sticks that are required for

 *			a single memory access or all of the memory sticks

 *			spanned by a chip-select row.  A single socket set

 *			has two chip-select rows and if double-sided sticks

 *			are used these will occupy those chip-select rows.

 *

 * Bank:		This term is avoided because it is unclear when

 *			needing to distinguish between chip-select rows and

 *			socket sets.

 *

 * Controller pages:

 *

 * Physical pages:

 *

 * Virtual pages:

 *

 *

 * STRUCTURE ORGANIZATION AND CHOICES

 *

 *

 *

 * PS - I enjoyed writing all that about as much as you enjoyed reading it.

 */

/**

 * enum edac_mc_layer - memory controller hierarchy layer

 *