docs-rst: admin-guide: add documentation for EDAC

EDAC is part of the Kernel's RAS facilities, with is useful for
system admins to detect errors. So, add it to the admin's guide.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

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diff --git a/Documentation/admin-guide/ras.rst b/Documentation/admin-guide/ras.rst
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+.. include:: <isonum.txt>
+
+============================================
+Reliability, Availability and Serviceability
+============================================
+
+RAS concepts
+************
+
+Reliability, Availability and Serviceability (RAS) is a concept used on
+servers meant to measure their robusteness.
+
+Reliability
+  is the probability that a system will produce correct outputs.
+
+  * Generally measured as Mean Time Between Failures (MTBF)
+  * Enhanced by features that help to avoid, detect and repair hardware faults
+
+Availability
+  is the probability that a system is operational at a given time
+
+  * Generally measured as a percentage of downtime per a period of time
+  * Often uses mechanisms to detect and correct hardware faults in
+    runtime;
+
+Serviceability (or maintainability)
+  is the simplicity and speed with which a system can be repaired or
+  maintained
+
+  * Generally measured on Mean Time Between Repair (MTBR)
+
+Improving RAS
+-------------
+
+In order to reduce systems downtime, a system should be capable of detecting
+hardware errors, and, when possible correcting them in runtime. It should
+also provide mechanisms to detect hardware degradation, in order to warn
+the system administrator to take the action of replacing a component before
+it causes data loss or system downtime.
+
+Among the monitoring measures, the most usual ones include:
+
+* CPU – detect errors at instruction execution and at L1/L2/L3 caches;
+* Memory – add error correction logic (ECC) to detect and correct errors;
+* I/O – add CRC checksums for tranfered data;
+* Storage – RAID, journal file systems, checksums,
+  Self-Monitoring, Analysis and Reporting Technology (SMART).
+
+By monitoring the number of occurrences of error detections, it is possible
+to identify if the probability of hardware errors is increasing, and, on such
+case, do a preventive maintainance to replace a degrated component while
+those errors are correctable.
+
+Types of errors
+---------------
+
+Most mechanisms used on modern systems use use technologies like Hamming
+Codes that allow error correction when the number of errors on a bit packet
+is below a threshold. If the number of errors is above, those mechanisms
+can indicate with a high degree of confidence that an error happened, but
+they can't correct.
+
+Also, sometimes an error occur on a component that it is not used. For
+example, a part of the memory that it is not currently allocated.
+
+That defines some categories of errors:
+
+* **Correctable Error (CE)** - the error detection mechanism detected and
+  corrected the error. Such errors are usually not fatal, although some
+  Kernel mechanisms allow the system administrator to consider them as fatal.
+
+* **Uncorrected Error (UE)** - the amount of errors happened above the error
+  correction threshold, and the system was unable to auto-correct.
+
+* **Fatal Error** - when an UE error happens on a critical component of the
+  system (for example, a piece of the Kernel got corrupted by an UE), the
+  only reliable way to avoid data corruption is to hang or reboot the machine.
+
+* **Non-fatal Error** - when an UE error happens on an unused component,
+  like a CPU in power down state or an unused memory bank, the system may
+  still run, eventually replacing the affected hardware by a hot spare,
+  if available.
+
+  Also, when an error happens on an userspace process, it is also possible to
+  kill such process and let userspace restart it.
+
+The mechanism for handling non-fatal errors is usually complex and may
+require the help of some userspace application, in order to apply the
+policy desired by the system administrator.
+
+Identifying a bad hardware component
+------------------------------------
+
+Just detecting a hardware flaw is usually not enough, as the system needs
+to pinpoint to the minimal replaceable unit (MRU) that should be exchanged
+to make the hardware reliable again.
+
+So, it requires not only error logging facilities, but also mechanisms that
+will translate the error message to the silkscreen or component label for
+the MRU.
+
+Typically, it is very complex for memory, as modern CPUs interlace memory
+from different memory modules, in order to provide a better performance. The
+DMI BIOS usually have a list of memory module labels, with can be obtained
+using the ``dmidecode`` tool. For example, on a desktop machine, it shows::
+
+	Memory Device
+		Total Width: 64 bits
+		Data Width: 64 bits
+		Size: 16384 MB
+		Form Factor: SODIMM
+		Set: None
+		Locator: ChannelA-DIMM0
+		Bank Locator: BANK 0
+		Type: DDR4
+		Type Detail: Synchronous
+		Speed: 2133 MHz
+		Rank: 2
+		Configured Clock Speed: 2133 MHz
+
+On the above example, a DDR4 SO-DIMM memory module is located at the
+system's memory labeled as "BANK 0", as given by the *bank locator* field.
+Please notice that, on such system, the *total width* is equal to the
+*data witdh*. It means that such memory module doesn't have error
+detection/correction mechanisms.
+
+Unfortunately, not all systems use the same field to specify the memory
+bank. On this example, from an older server, ``dmidecode`` shows::
+
+	Memory Device
+		Array Handle: 0x1000
+		Error Information Handle: Not Provided
+		Total Width: 72 bits
+		Data Width: 64 bits
+		Size: 8192 MB
+		Form Factor: DIMM
+		Set: 1
+		Locator: DIMM_A1
+		Bank Locator: Not Specified
+		Type: DDR3
+		Type Detail: Synchronous Registered (Buffered)
+		Speed: 1600 MHz
+		Rank: 2
+		Configured Clock Speed: 1600 MHz
+
+There, the DDR3 RDIMM memory module is located at the system's memory labeled
+as "DIMM_A1", as given by the *locator* field. Please notice that this
+memory module has 64 bits of *data witdh* and 72 bits of *total width*. So,
+it has 8 extra bits to be used by error detection and correction mechanisms.
+Such kind of memory is called Error-correcting code memory (ECC memory).
+
+To make things even worse, it is not uncommon that systems with different
+labels on their system's board to use exactly the same BIOS, meaning that
+the labels provided by the BIOS won't match the real ones.
+
+ECC memory
+----------
+
+As mentioned on the previous section, ECC memory has extra bits to be
+used for error correction. So, on 64 bit systems, a memory module
+has 64 bits of *data width*, and 74 bits of *total width*. So, there are
+8 bits extra bits to be used for the error detection and correction
+mechanisms. Those extra bits are called *syndrome*\ [#f1]_\ [#f2]_.
+
+So, when the cpu requests the memory controller to write a word with
+*data width*, the memory controller calculates the *syndrome* in real time,
+using Hamming code, or some other error correction code, like SECDED+,
+producing a code with *total width* size. Such code is then written
+on the memory modules.
+
+At read, the *total width* bits code is converted back, using the same
+ECC code used on write, producing a word with *data width* and a *syndrome*.
+The word with *data width* is sent to the CPU, even when errors happen.
+
+The memory controller also looks at the *syndrome* in order to check if
+there was an error, and if the ECC code was able to fix such error.
+If the error was corrected, a Corrected Error (CE) happened. If not, an
+Uncorrected Error (UE) happened.
+
+The information about the CE/UE errors is stored on some special registers
+at the memory controller and can be accessed by reading such registers,
+either by BIOS, by some special CPUs or by Linux EDAC driver. On x86 64
+bit CPUs, such errors can also be retrieved via the Machine Check
+Architecture (MCA)\ [#f3]_.
+
+.. [#f1] Please notice that several memory controllers allow operation on a
+  mode called "Lock-Step", where it groups two memory modules together,
+  doing 128-bit reads/writes. That gives 16 bits for error correction, with
+  significatively improves the error correction mechanism, at the expense
+  that, when an error happens, there's no way to know what memory module is
+  to blame. So, it has to blame both memory modules.
+
+.. [#f2] Some memory controllers also allow using memory in mirror mode.
+  On such mode, the same data is written to two memory modules. At read,
+  the system checks both memory modules, in order to check if both provide
+  identical data. On such configuration, when an error happens, there's no
+  way to know what memory module is to blame. So, it has to blame both
+  memory modules (or 4 memory modules, if the system is also on Lock-step
+  mode).
+
+.. [#f3] For more details about the Machine Check Architecture (MCA),
+  please read Documentation/x86/x86_64/machinecheck at the Kernel tree.
+
+EDAC - Error Detection And Correction
+*************************************
+
+.. note::
+
+   "bluesmoke" was the name for this device driver subsystem when it
+   was "out-of-tree" and maintained at http://bluesmoke.sourceforge.net.
+   That site is mostly archaic now and can be used only for historical
+   purposes.
+
+   When the subsystem was pushed upstream for the first time, on
+   Kernel 2.6.16, for the first time, it was renamed to ``EDAC``.
+
+Purpose
+-------
+
+The ``edac`` kernel module's goal is to detect and report hardware errors
+that occur within the computer system running under linux.
+
+Memory
+------
+
+Memory Correctable Errors (CE) and Uncorrectable Errors (UE) are the
+primary errors being harvested. These types of errors are harvested by
+the ``edac_mc`` device.
+
+Detecting CE events, then harvesting those events and reporting them,
+**can** but must not necessarily be a predictor of future UE events. With
+CE events only, the system can and will continue to operate as no data
+has been damaged yet.
+
+However, preventive maintenance and proactive part replacement of memory
+modules exhibiting CEs can reduce the likelihood of the dreaded UE events
+and system panics.
+
+Other hardware elements
+-----------------------
+
+A new feature for EDAC, the ``edac_device`` class of device, was added in
+the 2.6.23 version of the kernel.
+
+This new device type allows for non-memory type of ECC hardware detectors
+to have their states harvested and presented to userspace via the sysfs
+interface.
+
+Some architectures have ECC detectors for L1, L2 and L3 caches,
+along with DMA engines, fabric switches, main data path switches,
+interconnections, and various other hardware data paths. If the hardware
+reports it, then a edac_device device probably can be constructed to
+harvest and present that to userspace.
+
+
+PCI bus scanning
+----------------
+
+In addition, PCI devices are scanned for PCI Bus Parity and SERR Errors
+in order to determine if errors are occurring during data transfers.
+
+The presence of PCI Parity errors must be examined with a grain of salt.
+There are several add-in adapters that do **not** follow the PCI specification
+with regards to Parity generation and reporting. The specification says
+the vendor should tie the parity status bits to 0 if they do not intend
+to generate parity.  Some vendors do not do this, and thus the parity bit
+can "float" giving false positives.
+
+There is a PCI device attribute located in sysfs that is checked by
+the EDAC PCI scanning code. If that attribute is set, PCI parity/error
+scanning is skipped for that device. The attribute is::
+
+	broken_parity_status
+
+and is located in ``/sys/devices/pci<XXX>/0000:XX:YY.Z`` directories for
+PCI devices.
+
+
+Versioning
+----------
+
+EDAC is composed of a "core" module (``edac_core.ko``) and several Memory
+Controller (MC) driver modules. On a given system, the CORE is loaded
+and one MC driver will be loaded. Both the CORE and the MC driver (or
+``edac_device`` driver) have individual versions that reflect current
+release level of their respective modules.
+
+Thus, to "report" on what version a system is running, one must report
+both the CORE's and the MC driver's versions.
+
+
+Loading
+-------
+
+If ``edac`` was statically linked with the kernel then no loading
+is necessary. If ``edac`` was built as modules then simply modprobe
+the ``edac`` pieces that you need. You should be able to modprobe
+hardware-specific modules and have the dependencies load the necessary
+core modules.
+
+Example::
+
+	$ modprobe amd76x_edac
+
+loads both the ``amd76x_edac.ko`` memory controller module and the
+``edac_mc.ko`` core module.
+
+
+Sysfs interface
+---------------
+
+EDAC presents a ``sysfs`` interface for control and reporting purposes. It
+lives in the /sys/devices/system/edac directory.
+
+Within this directory there currently reside 2 components:
+
+	======= ==============================
+	mc	memory controller(s) system
+	pci	PCI control and status system
+	======= ==============================
+
+
+
+Memory Controller (mc) Model
+----------------------------
+
+Each ``mc`` device controls a set of memory modules [#f4]_. These modules
+are laid out in a Chip-Select Row (``csrowX``) and Channel table (``chX``).
+There can be multiple csrows and multiple channels.
+
+.. [#f4] Nowadays, the term DIMM (Dual In-line Memory Module) is widely
+  used to refer to a memory module, although there are other memory
+  packaging alternatives, like SO-DIMM, SIMM, etc. Along this document,
+  and inside the EDAC system, the term "dimm" is used for all memory
+  modules, even when they use a different kind of packaging.
+
+Memory controllers allow for several csrows, with 8 csrows being a
+typical value. Yet, the actual number of csrows depends on the layout of
+a given motherboard, memory controller and memory module characteristics.
+
+Dual channels allow for dual data length (e. g. 128 bits, on 64 bit systems)
+data transfers to/from the CPU from/to memory. Some newer chipsets allow
+for more than 2 channels, like Fully Buffered DIMMs (FB-DIMMs) memory
+controllers. The following example will assume 2 channels:
+
+	+------------+-----------------------+
+	| Chip       |       Channels        |
+	| Select     +-----------+-----------+
+	| rows       |  ``ch0``  |  ``ch1``  |
+	+============+===========+===========+
+	| ``csrow0`` |  DIMM_A0  |  DIMM_B0  |
+	+------------+           |           |
+	| ``csrow1`` |           |           |
+	+------------+-----------+-----------+
+	| ``csrow2`` |  DIMM_A1  | DIMM_B1   |
+	+------------+           |           |
+	| ``csrow3`` |           |           |
+	+------------+-----------+-----------+
+
+In the above example, there are 4 physical slots on the motherboard
+for memory DIMMs:
+
+	+---------+---------+
+	| DIMM_A0 | DIMM_B0 |
+	+---------+---------+
+	| DIMM_A1 | DIMM_B1 |
+	+---------+---------+
+
+Labels for these slots are usually silk-screened on the motherboard.
+Slots labeled ``A`` are channel 0 in this example. Slots labeled ``B`` are
+channel 1. Notice that there are two csrows possible on a physical DIMM.
+These csrows are allocated their csrow assignment based on the slot into
+which the memory DIMM is placed. Thus, when 1 DIMM is placed in each
+Channel, the csrows cross both DIMMs.
+
+Memory DIMMs come single or dual "ranked". A rank is a populated csrow.
+Thus, 2 single ranked DIMMs, placed in slots DIMM_A0 and DIMM_B0 above
+will have just one csrow (csrow0). csrow1 will be empty. On the other
+hand, when 2 dual ranked DIMMs are similarly placed, then both csrow0
+and csrow1 will be populated. The pattern repeats itself for csrow2 and
+csrow3.
+
+The representation of the above is reflected in the directory
+tree in EDAC's sysfs interface. Starting in directory
+``/sys/devices/system/edac/mc``, each memory controller will be
+represented by its own ``mcX`` directory, where ``X`` is the
+index of the MC::
+
+	..../edac/mc/
+		   |
+		   |->mc0
+		   |->mc1
+		   |->mc2
+		   ....
+
+Under each ``mcX`` directory each ``csrowX`` is again represented by a
+``csrowX``, where ``X`` is the csrow index::
+
+	.../mc/mc0/
+		|
+		|->csrow0
+		|->csrow2
+		|->csrow3
+		....
+
+Notice that there is no csrow1, which indicates that csrow0 is composed
+of a single ranked DIMMs. This should also apply in both Channels, in
+order to have dual-channel mode be operational. Since both csrow2 and
+csrow3 are populated, this indicates a dual ranked set of DIMMs for
+channels 0 and 1.
+
+Within each of the ``mcX`` and ``csrowX`` directories are several EDAC
+control and attribute files.
+
+``mcX`` directories
+-------------------
+
+In ``mcX`` directories are EDAC control and attribute files for
+this ``X`` instance of the memory controllers.
+
+For a description of the sysfs API, please see:
+
+	Documentation/ABI/testing/sysfs-devices-edac
+
+
+``dimmX`` or ``rankX`` directories
+----------------------------------
+
+The recommended way to use the EDAC subsystem is to look at the information
+provided by the ``dimmX`` or ``rankX`` directories [#f5]_.
+
+A typical EDAC system has the following structure under
+``/sys/devices/system/edac/``\ [#f6]_::
+
+	/sys/devices/system/edac/
+	├── mc
+	│   ├── mc0
+	│   │   ├── ce_count
+	│   │   ├── ce_noinfo_count
+	│   │   ├── dimm0
+	│   │   │   ├── dimm_dev_type
+	│   │   │   ├── dimm_edac_mode
+	│   │   │   ├── dimm_label
+	│   │   │   ├── dimm_location
+	│   │   │   ├── dimm_mem_type
+	│   │   │   ├── size
+	│   │   │   └── uevent
+	│   │   ├── max_location
+	│   │   ├── mc_name
+	│   │   ├── reset_counters
+	│   │   ├── seconds_since_reset
+	│   │   ├── size_mb
+	│   │   ├── ue_count
+	│   │   ├── ue_noinfo_count
+	│   │   └── uevent
+	│   ├── mc1
+	│   │   ├── ce_count
+	│   │   ├── ce_noinfo_count
+	│   │   ├── dimm0
+	│   │   │   ├── dimm_dev_type
+	│   │   │   ├── dimm_edac_mode
+	│   │   │   ├── dimm_label
+	│   │   │   ├── dimm_location
+	│   │   │   ├── dimm_mem_type
+	│   │   │   ├── size
+	│   │   │   └── uevent
+	│   │   ├── max_location
+	│   │   ├── mc_name
+	│   │   ├── reset_counters
+	│   │   ├── seconds_since_reset
+	│   │   ├── size_mb
+	│   │   ├── ue_count
+	│   │   ├── ue_noinfo_count
+	│   │   └── uevent
+	│   └── uevent
+	└── uevent
+
+In the ``dimmX`` directories are EDAC control and attribute files for
+this ``X`` memory module:
+
+- ``size`` - Total memory managed by this csrow attribute file
+
+	This attribute file displays, in count of megabytes, the memory
+	that this csrow contains.
+
+- ``dimm_dev_type``  - Device type attribute file
+
+	This attribute file will display what type of DRAM device is
+	being utilized on this DIMM.
+	Examples:
+
+		- x1
+		- x2
+		- x4
+		- x8
+
+- ``dimm_edac_mode`` - EDAC Mode of operation attribute file
+
+	This attribute file will display what type of Error detection
+	and correction is being utilized.
+
+- ``dimm_label`` - memory module label control file
+
+	This control file allows this DIMM to have a label assigned
+	to it. With this label in the module, when errors occur
+	the output can provide the DIMM label in the system log.
+	This becomes vital for panic events to isolate the
+	cause of the UE event.
+
+	DIMM Labels must be assigned after booting, with information
+	that correctly identifies the physical slot with its
+	silk screen label. This information is currently very
+	motherboard specific and determination of this information
+	must occur in userland at this time.
+
+- ``dimm_location`` - location of the memory module
+
+	The location can have up to 3 levels, and describe how the
+	memory controller identifies the location of a memory module.
+	Depending on the type of memory and memory controller, it
+	can be:
+
+		- *csrow* and *channel* - used when the memory controller
+		  doesn't identify a single DIMM - e. g. in ``rankX`` dir;
+		- *branch*, *channel*, *slot* - typically used on FB-DIMM memory
+		  controllers;
+		- *channel*, *slot* - used on Nehalem and newer Intel drivers.
+
+- ``dimm_mem_type`` - Memory Type attribute file
+
+	This attribute file will display what type of memory is currently
+	on this csrow. Normally, either buffered or unbuffered memory.
+	Examples:
+
+		- Registered-DDR
+		- Unbuffered-DDR
+
+.. [#f5] On some systems, the memory controller doesn't have any logic
+  to identify the memory module. On such systems, the directory is called ``rankX`` and works on a similar way as the ``csrowX`` directories.
+  On modern Intel memory controllers, the memory controller identifies the
+  memory modules directly. On such systems, the directory is called ``dimmX``.
+
+.. [#f6] There are also some ``power`` directories and ``subsystem``
+  symlinks inside the sysfs mapping that are automatically created by
+  the sysfs subsystem. Currently, they serve no purpose.
+
+``csrowX`` directories
+----------------------
+
+When CONFIG_EDAC_LEGACY_SYSFS is enabled, sysfs will contain the ``csrowX``
+directories. As this API doesn't work properly for Rambus, FB-DIMMs and
+modern Intel Memory Controllers, this is being deprecated in favor of
+``dimmX`` directories.
+
+In the ``csrowX`` directories are EDAC control and attribute files for
+this ``X`` instance of csrow:
+
+
+- ``ue_count`` - Total Uncorrectable Errors count attribute file
+
+	This attribute file displays the total count of uncorrectable
+	errors that have occurred on this csrow. If panic_on_ue is set
+	this counter will not have a chance to increment, since EDAC
+	will panic the system.
+
+
+- ``ce_count`` - Total Correctable Errors count attribute file
+
+	This attribute file displays the total count of correctable
+	errors that have occurred on this csrow. This count is very
+	important to examine. CEs provide early indications that a
+	DIMM is beginning to fail. This count field should be
+	monitored for non-zero values and report such information
+	to the system administrator.
+
+
+- ``size_mb`` - Total memory managed by this csrow attribute file
+
+	This attribute file displays, in count of megabytes, the memory
+	that this csrow contains.
+
+
+- ``mem_type`` - Memory Type attribute file
+
+	This attribute file will display what type of memory is currently
+	on this csrow. Normally, either buffered or unbuffered memory.
+	Examples:
+
+		- Registered-DDR
+		- Unbuffered-DDR
+
+
+- ``edac_mode`` - EDAC Mode of operation attribute file
+
+	This attribute file will display what type of Error detection
+	and correction is being utilized.
+
+
+- ``dev_type`` - Device type attribute file
+
+	This attribute file will display what type of DRAM device is
+	being utilized on this DIMM.
+	Examples:
+
+		- x1
+		- x2
+		- x4
+		- x8
+
+
+- ``ch0_ce_count`` - Channel 0 CE Count attribute file
+
+	This attribute file will display the count of CEs on this
+	DIMM located in channel 0.
+
+
+- ``ch0_ue_count`` - Channel 0 UE Count attribute file
+
+	This attribute file will display the count of UEs on this
+	DIMM located in channel 0.
+
+
+- ``ch0_dimm_label`` - Channel 0 DIMM Label control file
+
+
+	This control file allows this DIMM to have a label assigned
+	to it. With this label in the module, when errors occur
+	the output can provide the DIMM label in the system log.
+	This becomes vital for panic events to isolate the
+	cause of the UE event.
+
+	DIMM Labels must be assigned after booting, with information
+	that correctly identifies the physical slot with its
+	silk screen label. This information is currently very
+	motherboard specific and determination of this information
+	must occur in userland at this time.
+
+
+- ``ch1_ce_count`` - Channel 1 CE Count attribute file
+
+
+	This attribute file will display the count of CEs on this
+	DIMM located in channel 1.
+
+
+- ``ch1_ue_count`` - Channel 1 UE Count attribute file
+
+
+	This attribute file will display the count of UEs on this
+	DIMM located in channel 0.
+
+
+- ``ch1_dimm_label`` - Channel 1 DIMM Label control file
+
+	This control file allows this DIMM to have a label assigned
+	to it. With this label in the module, when errors occur
+	the output can provide the DIMM label in the system log.
+	This becomes vital for panic events to isolate the
+	cause of the UE event.
+
+	DIMM Labels must be assigned after booting, with information
+	that correctly identifies the physical slot with its
+	silk screen label. This information is currently very
+	motherboard specific and determination of this information
+	must occur in userland at this time.
+
+
+System Logging
+--------------
+
+If logging for UEs and CEs is enabled, then system logs will contain
+information indicating that errors have been detected::
+
+  EDAC MC0: CE page 0x283, offset 0xce0, grain 8, syndrome 0x6ec3, row 0, channel 1 "DIMM_B1": amd76x_edac
+  EDAC MC0: CE page 0x1e5, offset 0xfb0, grain 8, syndrome 0xb741, row 0, channel 1 "DIMM_B1": amd76x_edac
+
+
+The structure of the message is:
+
+	+---------------------------------------+-------------+
+	| Content                               + Example     |
+	+=======================================+=============+
+	| The memory controller                 | MC0         |
+	+---------------------------------------+-------------+
+	| Error type                            | CE          |
+	+---------------------------------------+-------------+
+	| Memory page                           | 0x283       |
+	+---------------------------------------+-------------+
+	| Offset in the page                    | 0xce0       |
+	+---------------------------------------+-------------+
+	| The byte granularity                  | grain 8     |
+	| or resolution of the error            |             |
+	+---------------------------------------+-------------+
+	| The error syndrome                    | 0xb741      |
+	+---------------------------------------+-------------+
+	| Memory row                            | row 0       +
+	+---------------------------------------+-------------+
+	| Memory channel                        | channel 1   |
+	+---------------------------------------+-------------+
+	| DIMM label, if set prior              | DIMM B1     |
+	+---------------------------------------+-------------+
+	| And then an optional, driver-specific |             |
+	| message that may have additional      |             |
+	| information.                          |             |
+	+---------------------------------------+-------------+
+
+Both UEs and CEs with no info will lack all but memory controller, error
+type, a notice of "no info" and then an optional, driver-specific error
+message.
+
+
+PCI Bus Parity Detection
+------------------------
+
+On Header Type 00 devices, the primary status is looked at for any
+parity error regardless of whether parity is enabled on the device or
+not. (The spec indicates parity is generated in some cases). On Header
+Type 01 bridges, the secondary status register is also looked at to see
+if parity occurred on the bus on the other side of the bridge.
+
+
+Sysfs configuration
+-------------------
+
+Under ``/sys/devices/system/edac/pci`` are control and attribute files as
+follows:
+
+
+- ``check_pci_parity`` - Enable/Disable PCI Parity checking control file
+
+	This control file enables or disables the PCI Bus Parity scanning
+	operation. Writing a 1 to this file enables the scanning. Writing
+	a 0 to this file disables the scanning.
+
+	Enable::
+
+		echo "1" >/sys/devices/system/edac/pci/check_pci_parity
+
+	Disable::
+
+		echo "0" >/sys/devices/system/edac/pci/check_pci_parity
+
+
+- ``pci_parity_count`` - Parity Count
+
+	This attribute file will display the number of parity errors that
+	have been detected.
+
+
+Module parameters
+-----------------
+
+- ``edac_mc_panic_on_ue`` - Panic on UE control file
+
+	An uncorrectable error will cause a machine panic.  This is usually
+	desirable.  It is a bad idea to continue when an uncorrectable error
+	occurs - it is indeterminate what was uncorrected and the operating
+	system context might be so mangled that continuing will lead to further
+	corruption. If the kernel has MCE configured, then EDAC will never
+	notice the UE.
+
+	LOAD TIME::
+
+		module/kernel parameter: edac_mc_panic_on_ue=[0|1]
+
+	RUN TIME::
+
+		echo "1" > /sys/module/edac_core/parameters/edac_mc_panic_on_ue
+
+
+- ``edac_mc_log_ue`` - Log UE control file
+
+
+	Generate kernel messages describing uncorrectable errors.  These errors
+	are reported through the system message log system.  UE statistics
+	will be accumulated even when UE logging is disabled.
+
+	LOAD TIME::
+
+		module/kernel parameter: edac_mc_log_ue=[0|1]
+
+	RUN TIME::
+
+		echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ue
+
+
+- ``edac_mc_log_ce`` - Log CE control file
+
+
+	Generate kernel messages describing correctable errors.  These
+	errors are reported through the system message log system.
+	CE statistics will be accumulated even when CE logging is disabled.
+
+	LOAD TIME::
+
+		module/kernel parameter: edac_mc_log_ce=[0|1]
+
+	RUN TIME::
+
+		echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ce
+
+
+- ``edac_mc_poll_msec`` - Polling period control file
+
+
+	The time period, in milliseconds, for polling for error information.
+	Too small a value wastes resources.  Too large a value might delay
+	necessary handling of errors and might loose valuable information for
+	locating the error.  1000 milliseconds (once each second) is the current
+	default. Systems which require all the bandwidth they can get, may
+	increase this.
+
+	LOAD TIME::
+
+		module/kernel parameter: edac_mc_poll_msec=[0|1]
+
+	RUN TIME::
+
+		echo "1000" > /sys/module/edac_core/parameters/edac_mc_poll_msec
+
+
+- ``panic_on_pci_parity`` - Panic on PCI PARITY Error
+
+
+	This control file enables or disables panicking when a parity
+	error has been detected.
+
+
+	module/kernel parameter::
+
+			edac_panic_on_pci_pe=[0|1]
+
+	Enable::
+
+		echo "1" > /sys/module/edac_core/parameters/edac_panic_on_pci_pe
+
+	Disable::
+
+		echo "0" > /sys/module/edac_core/parameters/edac_panic_on_pci_pe
+
+
+
+EDAC device type
+----------------
+
+In the header file, edac_core.h, there is a series of edac_device structures
+and APIs for the EDAC_DEVICE.
+
+User space access to an edac_device is through the sysfs interface.
+
+At the location ``/sys/devices/system/edac`` (sysfs) new edac_device devices
+will appear.
+
+There is a three level tree beneath the above ``edac`` directory. For example,
+the ``test_device_edac`` device (found at the http://bluesmoke.sourceforget.net
+website) installs itself as::
+
+	/sys/devices/system/edac/test-instance
+
+in this directory are various controls, a symlink and one or more ``instance``
+directories.
+
+The standard default controls are:
+
+	==============	=======================================================
+	log_ce		boolean to log CE events
+	log_ue		boolean to log UE events
+	panic_on_ue	boolean to ``panic`` the system if an UE is encountered
+			(default off, can be set true via startup script)
+	poll_msec	time period between POLL cycles for events
+	==============	=======================================================
+
+The test_device_edac device adds at least one of its own custom control:
+
+	==============	==================================================
+	test_bits	which in the current test driver does nothing but
+			show how it is installed. A ported driver can
+			add one or more such controls and/or attributes
+			for specific uses.
+			One out-of-tree driver uses controls here to allow
+			for ERROR INJECTION operations to hardware
+			injection registers
+	==============	==================================================
+
+The symlink points to the 'struct dev' that is registered for this edac_device.
+
+Instances
+---------
+
+One or more instance directories are present. For the ``test_device_edac``
+case:
+
+	+----------------+
+	| test-instance0 |
+	+----------------+
+
+
+In this directory there are two default counter attributes, which are totals of
+counter in deeper subdirectories.
+
+	==============	====================================
+	ce_count	total of CE events of subdirectories
+	ue_count	total of UE events of subdirectories
+	==============	====================================
+
+Blocks
+------
+
+At the lowest directory level is the ``block`` directory. There can be 0, 1
+or more blocks specified in each instance:
+
+	+-------------+
+	| test-block0 |
+	+-------------+
+
+In this directory the default attributes are:
+
+	==============	================================================
+	ce_count	which is counter of CE events for this ``block``
+			of hardware being monitored
+	ue_count	which is counter of UE events for this ``block``
+			of hardware being monitored
+	==============	================================================
+
+
+The ``test_device_edac`` device adds 4 attributes and 1 control:
+
+	================== ====================================================
+	test-block-bits-0	for every POLL cycle this counter
+				is incremented
+	test-block-bits-1	every 10 cycles, this counter is bumped once,
+				and test-block-bits-0 is set to 0
+	test-block-bits-2	every 100 cycles, this counter is bumped once,
+				and test-block-bits-1 is set to 0
+	test-block-bits-3	every 1000 cycles, this counter is bumped once,
+				and test-block-bits-2 is set to 0
+	================== ====================================================
+
+
+	================== ====================================================
+	reset-counters		writing ANY thing to this control will
+				reset all the above counters.
+	================== ====================================================
+
+
+Use of the ``test_device_edac`` driver should enable any others to create their own
+unique drivers for their hardware systems.
+
+The ``test_device_edac`` sample driver is located at the
+http://bluesmoke.sourceforge.net project site for EDAC.
+
+
+Usage of EDAC APIs on Nehalem and newer Intel CPUs
+--------------------------------------------------
+
+On older Intel architectures, the memory controller was part of the North
+Bridge chipset. Nehalem, Sandy Bridge, Ivy Bridge, Haswell, Sky Lake and
+newer Intel architectures integrated an enhanced version of the memory
+controller (MC) inside the CPUs.
+
+This chapter will cover the differences of the enhanced memory controllers
+found on newer Intel CPUs, such as ``i7core_edac``, ``sb_edac`` and
+``sbx_edac`` drivers.
+
+.. note::
+
+   The Xeon E7 processor families use a separate chip for the memory
+   controller, called Intel Scalable Memory Buffer. This section doesn't
+   apply for such families.
+
+1) There is one Memory Controller per Quick Patch Interconnect
+   (QPI). At the driver, the term "socket" means one QPI. This is
+   associated with a physical CPU socket.
+
+   Each MC have 3 physical read channels, 3 physical write channels and
+   3 logic channels. The driver currently sees it as just 3 channels.
+   Each channel can have up to 3 DIMMs.
+
+   The minimum known unity is DIMMs. There are no information about csrows.
+   As EDAC API maps the minimum unity is csrows, the driver sequentially
+   maps channel/DIMM into different csrows.
+
+   For example, supposing the following layout::
+
+	Ch0 phy rd0, wr0 (0x063f4031): 2 ranks, UDIMMs
+	  dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
+	  dimm 1 1024 Mb offset: 4, bank: 8, rank: 1, row: 0x4000, col: 0x400
+        Ch1 phy rd1, wr1 (0x063f4031): 2 ranks, UDIMMs
+	  dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
+	Ch2 phy rd3, wr3 (0x063f4031): 2 ranks, UDIMMs
+	  dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
+
+   The driver will map it as::
+
+	csrow0: channel 0, dimm0
+	csrow1: channel 0, dimm1
+	csrow2: channel 1, dimm0
+	csrow3: channel 2, dimm0
+
+   exports one DIMM per csrow.
+
+   Each QPI is exported as a different memory controller.
+
+2) The MC has the ability to inject errors to test drivers. The drivers
+   implement this functionality via some error injection nodes:
+
+   For injecting a memory error, there are some sysfs nodes, under
+   ``/sys/devices/system/edac/mc/mc?/``:
+
+   - ``inject_addrmatch/*``:
+      Controls the error injection mask register. It is possible to specify
+      several characteristics of the address to match an error code::
+
+         dimm = the affected dimm. Numbers are relative to a channel;
+         rank = the memory rank;
+         channel = the channel that will generate an error;
+         bank = the affected bank;
+         page = the page address;
+         column (or col) = the address column.
+
+      each of the above values can be set to "any" to match any valid value.
+
+      At driver init, all values are set to any.
+
+      For example, to generate an error at rank 1 of dimm 2, for any channel,
+      any bank, any page, any column::
+
+		echo 2 >/sys/devices/system/edac/mc/mc0/inject_addrmatch/dimm
+		echo 1 >/sys/devices/system/edac/mc/mc0/inject_addrmatch/rank
+
+	To return to the default behaviour of matching any, you can do::
+
+		echo any >/sys/devices/system/edac/mc/mc0/inject_addrmatch/dimm
+		echo any >/sys/devices/system/edac/mc/mc0/inject_addrmatch/rank
+
+   - ``inject_eccmask``:
+          specifies what bits will have troubles,
+
+   - ``inject_section``:
+       specifies what ECC cache section will get the error::
+
+		3 for both
+		2 for the highest
+		1 for the lowest
+
+   - ``inject_type``:
+       specifies the type of error, being a combination of the following bits::
+
+		bit 0 - repeat
+		bit 1 - ecc
+		bit 2 - parity
+
+   - ``inject_enable``:
+       starts the error generation when something different than 0 is written.
+
+   All inject vars can be read. root permission is needed for write.
+
+   Datasheet states that the error will only be generated after a write on an
+   address that matches inject_addrmatch. It seems, however, that reading will
+   also produce an error.
+
+   For example, the following code will generate an error for any write access
+   at socket 0, on any DIMM/address on channel 2::
+
+	echo 2 >/sys/devices/system/edac/mc/mc0/inject_addrmatch/channel
+	echo 2 >/sys/devices/system/edac/mc/mc0/inject_type
+	echo 64 >/sys/devices/system/edac/mc/mc0/inject_eccmask
+	echo 3 >/sys/devices/system/edac/mc/mc0/inject_section
+	echo 1 >/sys/devices/system/edac/mc/mc0/inject_enable
+	dd if=/dev/mem of=/dev/null seek=16k bs=4k count=1 >& /dev/null
+
+   For socket 1, it is needed to replace "mc0" by "mc1" at the above
+   commands.
+
+   The generated error message will look like::
+
+	EDAC MC0: UE row 0, channel-a= 0 channel-b= 0 labels "-": NON_FATAL (addr = 0x0075b980, socket=0, Dimm=0, Channel=2, syndrome=0x00000040, count=1, Err=8c0000400001009f:4000080482 (read error: read ECC error))
+
+3) Corrected Error memory register counters
+
+   Those newer MCs have some registers to count memory errors. The driver
+   uses those registers to report Corrected Errors on devices with Registered
+   DIMMs.
+
+   However, those counters don't work with Unregistered DIMM. As the chipset
+   offers some counters that also work with UDIMMs (but with a worse level of
+   granularity than the default ones), the driver exposes those registers for
+   UDIMM memories.
+
+   They can be read by looking at the contents of ``all_channel_counts/``::
+
+     $ for i in /sys/devices/system/edac/mc/mc0/all_channel_counts/*; do echo $i; cat $i; done
+	/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm0
+	0
+	/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm1
+	0
+	/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm2
+	0
+
+   What happens here is that errors on different csrows, but at the same
+   dimm number will increment the same counter.
+   So, in this memory mapping::
+
+	csrow0: channel 0, dimm0
+	csrow1: channel 0, dimm1
+	csrow2: channel 1, dimm0
+	csrow3: channel 2, dimm0
+
+   The hardware will increment udimm0 for an error at the first dimm at either
+   csrow0, csrow2  or csrow3;
+
+   The hardware will increment udimm1 for an error at the second dimm at either
+   csrow0, csrow2  or csrow3;
+
+   The hardware will increment udimm2 for an error at the third dimm at either
+   csrow0, csrow2  or csrow3;
+
+4) Standard error counters
+
+   The standard error counters are generated when an mcelog error is received
+   by the driver. Since, with UDIMM, this is counted by software, it is
+   possible that some errors could be lost. With RDIMM's, they display the
+   contents of the registers
+
+Reference documents used on ``amd64_edac``
+------------------------------------------
+
+``amd64_edac`` module is based on the following documents
+(available from http://support.amd.com/en-us/search/tech-docs):
+
+1. :Title:  BIOS and Kernel Developer's Guide for AMD Athlon 64 and AMD
+	   Opteron Processors
+   :AMD publication #: 26094
+   :Revision: 3.26
+   :Link: http://support.amd.com/TechDocs/26094.PDF
+
+2. :Title:  BIOS and Kernel Developer's Guide for AMD NPT Family 0Fh
+	   Processors
+   :AMD publication #: 32559
+   :Revision: 3.00
+   :Issue Date: May 2006
+   :Link: http://support.amd.com/TechDocs/32559.pdf
+
+3. :Title:  BIOS and Kernel Developer's Guide (BKDG) For AMD Family 10h
+	   Processors
+   :AMD publication #: 31116
+   :Revision: 3.00
+   :Issue Date: September 07, 2007
+   :Link: http://support.amd.com/TechDocs/31116.pdf
+
+4. :Title: BIOS and Kernel Developer's Guide (BKDG) for AMD Family 15h
+	  Models 30h-3Fh Processors
+   :AMD publication #: 49125
+   :Revision: 3.06
+   :Issue Date: 2/12/2015 (latest release)
+   :Link: http://support.amd.com/TechDocs/49125_15h_Models_30h-3Fh_BKDG.pdf
+
+5. :Title: BIOS and Kernel Developer's Guide (BKDG) for AMD Family 15h
+	  Models 60h-6Fh Processors
+   :AMD publication #: 50742
+   :Revision: 3.01
+   :Issue Date: 7/23/2015 (latest release)
+   :Link: http://support.amd.com/TechDocs/50742_15h_Models_60h-6Fh_BKDG.pdf
+
+6. :Title: BIOS and Kernel Developer's Guide (BKDG) for AMD Family 16h
+	  Models 00h-0Fh Processors
+   :AMD publication #: 48751
+   :Revision: 3.03
+   :Issue Date: 2/23/2015 (latest release)
+   :Link: http://support.amd.com/TechDocs/48751_16h_bkdg.pdf
+
+Credits
+=======
+
+* Written by Doug Thompson <dougthompson@xmission.com>
+
+  - 7 Dec 2005
+  - 17 Jul 2007	Updated
+
+* |copy| Mauro Carvalho Chehab
+
+  - 05 Aug 2009	Nehalem interface
+  - 26 Oct 2016 Converted to ReST and cleanups at the Nehalem section
+
+* EDAC authors/maintainers:
+
+  - Doug Thompson, Dave Jiang, Dave Peterson et al,
+  - Mauro Carvalho Chehab
+  - Borislav Petkov
+  - original author: Thayne Harbaugh