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EDAC: Update Documentation/edac.txt
Do some initial cleanup, more probably will come. - Move credits section to the end - Update maintainers - Drop sourceforge reference - project is long upstream now - Reformat sections - Reformat paragraphs - Clarify text - Bring it up-to-date - Drop useless "future hardware scanning" section Signed-off-by: Borislav Petkov <bp@suse.de>
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Borislav Petkov
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@ -1,53 +1,34 @@
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EDAC - Error Detection And Correction
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Written by Doug Thompson <dougthompson@xmission.com>
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7 Dec 2005
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17 Jul 2007 Updated
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(c) Mauro Carvalho Chehab
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05 Aug 2009 Nehalem interface
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EDAC is maintained and written by:
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Doug Thompson, Dave Jiang, Dave Peterson et al,
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original author: Thayne Harbaugh,
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Contact:
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website: bluesmoke.sourceforge.net
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mailing list: bluesmoke-devel@lists.sourceforge.net
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=====================================
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"bluesmoke" was the name for this device driver when it was "out-of-tree"
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and maintained at sourceforge.net. When it was pushed into 2.6.16 for the
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first time, it was renamed to 'EDAC'.
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The bluesmoke project at sourceforge.net is now utilized as a 'staging area'
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for EDAC development, before it is sent upstream to kernel.org
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PURPOSE
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-------
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At the bluesmoke/EDAC project site, there is a series of quilt patches against
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recent kernels, stored in a SVN repository. For easier downloading, there
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is also a tarball snapshot available.
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============================================================================
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EDAC PURPOSE
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The 'edac' kernel module goal is to detect and report errors that occur
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within the computer system running under linux.
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The 'edac' kernel module's goal is to detect and report hardware errors
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that occur within the computer system running under linux.
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MEMORY
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------
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In the initial release, memory Correctable Errors (CE) and Uncorrectable
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Errors (UE) are the primary errors being harvested. These types of errors
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are harvested by the 'edac_mc' class of device.
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Memory Correctable Errors (CE) and Uncorrectable Errors (UE) are the
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primary errors being harvested. These types of errors are harvested by
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the 'edac_mc' device.
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Detecting CE events, then harvesting those events and reporting them,
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CAN be a predictor of future UE events. With CE events, the system can
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continue to operate, but with less safety. Preventive maintenance and
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proactive part replacement of memory DIMMs exhibiting CEs can reduce
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the likelihood of the dreaded UE events and system 'panics'.
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*can* but must not necessarily be a predictor of future UE events. With
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CE events only, the system can and will continue to operate as no data
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has been damaged yet.
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NON-MEMORY
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However, preventive maintenance and proactive part replacement of memory
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DIMMs exhibiting CEs can reduce the likelihood of the dreaded UE events
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and system panics.
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OTHER HARDWARE ELEMENTS
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-----------------------
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A new feature for EDAC, the edac_device class of device, was added in
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the 2.6.23 version of the kernel.
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@ -56,70 +37,57 @@ This new device type allows for non-memory type of ECC hardware detectors
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to have their states harvested and presented to userspace via the sysfs
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interface.
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Some architectures have ECC detectors for L1, L2 and L3 caches, along with DMA
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engines, fabric switches, main data path switches, interconnections,
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and various other hardware data paths. If the hardware reports it, then
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a edac_device device probably can be constructed to harvest and present
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that to userspace.
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Some architectures have ECC detectors for L1, L2 and L3 caches,
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along with DMA engines, fabric switches, main data path switches,
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interconnections, and various other hardware data paths. If the hardware
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reports it, then a edac_device device probably can be constructed to
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harvest and present that to userspace.
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PCI BUS SCANNING
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----------------
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In addition, PCI Bus Parity and SERR Errors are scanned for on PCI devices
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in order to determine if errors are occurring on data transfers.
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In addition, PCI devices are scanned for PCI Bus Parity and SERR Errors
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in order to determine if errors are occurring during data transfers.
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The presence of PCI Parity errors must be examined with a grain of salt.
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There are several add-in adapters that do NOT follow the PCI specification
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There are several add-in adapters that do *not* follow the PCI specification
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with regards to Parity generation and reporting. The specification says
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the vendor should tie the parity status bits to 0 if they do not intend
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to generate parity. Some vendors do not do this, and thus the parity bit
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can "float" giving false positives.
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In the kernel there is a PCI device attribute located in sysfs that is
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checked by the EDAC PCI scanning code. If that attribute is set,
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PCI parity/error scanning is skipped for that device. The attribute
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is:
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There is a PCI device attribute located in sysfs that is checked by
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the EDAC PCI scanning code. If that attribute is set, PCI parity/error
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scanning is skipped for that device. The attribute is:
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broken_parity_status
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as is located in /sys/devices/pci<XXX>/0000:XX:YY.Z directories for
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and is located in /sys/devices/pci<XXX>/0000:XX:YY.Z directories for
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PCI devices.
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FUTURE HARDWARE SCANNING
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EDAC will have future error detectors that will be integrated with
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EDAC or added to it, in the following list:
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MCE Machine Check Exception
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MCA Machine Check Architecture
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NMI NMI notification of ECC errors
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MSRs Machine Specific Register error cases
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and other mechanisms.
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These errors are usually bus errors, ECC errors, thermal throttling
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and the like.
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============================================================================
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EDAC VERSIONING
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VERSIONING
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----------
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EDAC is composed of a "core" module (edac_core.ko) and several Memory
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Controller (MC) driver modules. On a given system, the CORE
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is loaded and one MC driver will be loaded. Both the CORE and
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the MC driver (or edac_device driver) have individual versions that reflect
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current release level of their respective modules.
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Controller (MC) driver modules. On a given system, the CORE is loaded
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and one MC driver will be loaded. Both the CORE and the MC driver (or
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edac_device driver) have individual versions that reflect current
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release level of their respective modules.
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Thus, to "report" on what version a system is running, one must report both
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the CORE's and the MC driver's versions.
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Thus, to "report" on what version a system is running, one must report
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both the CORE's and the MC driver's versions.
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LOADING
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-------
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If 'edac' was statically linked with the kernel then no loading is
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necessary. If 'edac' was built as modules then simply modprobe the
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'edac' pieces that you need. You should be able to modprobe
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hardware-specific modules and have the dependencies load the necessary core
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modules.
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If 'edac' was statically linked with the kernel then no loading
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is necessary. If 'edac' was built as modules then simply modprobe
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the 'edac' pieces that you need. You should be able to modprobe
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hardware-specific modules and have the dependencies load the necessary
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core modules.
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Example:
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@ -129,35 +97,33 @@ loads both the amd76x_edac.ko memory controller module and the edac_mc.ko
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core module.
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============================================================================
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EDAC sysfs INTERFACE
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SYSFS INTERFACE
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---------------
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EDAC presents a 'sysfs' interface for control, reporting and attribute
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reporting purposes.
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EDAC presents a 'sysfs' interface for control and reporting purposes. It
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lives in the /sys/devices/system/edac directory.
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EDAC lives in the /sys/devices/system/edac directory.
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Within this directory there currently reside 2 'edac' components:
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Within this directory there currently reside 2 components:
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mc memory controller(s) system
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pci PCI control and status system
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============================================================================
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Memory Controller (mc) Model
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----------------------------
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First a background on the memory controller's model abstracted in EDAC.
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Each 'mc' device controls a set of DIMM memory modules. These modules are
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laid out in a Chip-Select Row (csrowX) and Channel table (chX). There can
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be multiple csrows and multiple channels.
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Each 'mc' device controls a set of DIMM memory modules. These modules
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are laid out in a Chip-Select Row (csrowX) and Channel table (chX).
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There can be multiple csrows and multiple channels.
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Memory controllers allow for several csrows, with 8 csrows being a typical value.
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Yet, the actual number of csrows depends on the electrical "loading"
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of a given motherboard, memory controller and DIMM characteristics.
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Memory controllers allow for several csrows, with 8 csrows being a
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typical value. Yet, the actual number of csrows depends on the layout of
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a given motherboard, memory controller and DIMM characteristics.
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Dual channels allows for 128 bit data transfers to the CPU from memory.
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Some newer chipsets allow for more than 2 channels, like Fully Buffered DIMMs
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(FB-DIMMs). The following example will assume 2 channels:
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Dual channels allows for 128 bit data transfers to/from the CPU from/to
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memory. Some newer chipsets allow for more than 2 channels, like Fully
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Buffered DIMMs (FB-DIMMs). The following example will assume 2 channels:
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Channel 0 Channel 1
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@ -179,12 +145,12 @@ for memory DIMMs:
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DIMM_A1
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DIMM_B1
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Labels for these slots are usually silk screened on the motherboard. Slots
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labeled 'A' are channel 0 in this example. Slots labeled 'B'
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are channel 1. Notice that there are two csrows possible on a
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physical DIMM. These csrows are allocated their csrow assignment
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based on the slot into which the memory DIMM is placed. Thus, when 1 DIMM
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is placed in each Channel, the csrows cross both DIMMs.
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Labels for these slots are usually silk-screened on the motherboard.
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Slots labeled 'A' are channel 0 in this example. Slots labeled 'B' are
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channel 1. Notice that there are two csrows possible on a physical DIMM.
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These csrows are allocated their csrow assignment based on the slot into
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which the memory DIMM is placed. Thus, when 1 DIMM is placed in each
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Channel, the csrows cross both DIMMs.
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Memory DIMMs come single or dual "ranked". A rank is a populated csrow.
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Thus, 2 single ranked DIMMs, placed in slots DIMM_A0 and DIMM_B0 above
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@ -193,8 +159,8 @@ when 2 dual ranked DIMMs are similarly placed, then both csrow0 and
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csrow1 will be populated. The pattern repeats itself for csrow2 and
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csrow3.
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The representation of the above is reflected in the directory tree
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in EDAC's sysfs interface. Starting in directory
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The representation of the above is reflected in the directory
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tree in EDAC's sysfs interface. Starting in directory
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/sys/devices/system/edac/mc each memory controller will be represented
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by its own 'mcX' directory, where 'X' is the index of the MC.
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@ -217,19 +183,19 @@ Under each 'mcX' directory each 'csrowX' is again represented by a
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|->csrow3
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....
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Notice that there is no csrow1, which indicates that csrow0 is
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composed of a single ranked DIMMs. This should also apply in both
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Channels, in order to have dual-channel mode be operational. Since
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both csrow2 and csrow3 are populated, this indicates a dual ranked
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set of DIMMs for channels 0 and 1.
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Notice that there is no csrow1, which indicates that csrow0 is composed
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of a single ranked DIMMs. This should also apply in both Channels, in
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order to have dual-channel mode be operational. Since both csrow2 and
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csrow3 are populated, this indicates a dual ranked set of DIMMs for
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channels 0 and 1.
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Within each of the 'mcX' and 'csrowX' directories are several
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EDAC control and attribute files.
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Within each of the 'mcX' and 'csrowX' directories are several EDAC
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control and attribute files.
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============================================================================
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'mcX' DIRECTORIES
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'mcX' directories
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-----------------
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In 'mcX' directories are EDAC control and attribute files for
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this 'X' instance of the memory controllers.
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@ -238,13 +204,14 @@ For a description of the sysfs API, please see:
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Documentation/ABI/testing/sysfs-devices-edac
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============================================================================
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'csrowX' DIRECTORIES
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When CONFIG_EDAC_LEGACY_SYSFS is enabled, the sysfs will contain the
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csrowX directories. As this API doesn't work properly for Rambus, FB-DIMMs
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and modern Intel Memory Controllers, this is being deprecated in favor
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of dimmX directories.
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'csrowX' directories
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--------------------
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When CONFIG_EDAC_LEGACY_SYSFS is enabled, sysfs will contain the csrowX
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directories. As this API doesn't work properly for Rambus, FB-DIMMs and
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modern Intel Memory Controllers, this is being deprecated in favor of
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dimmX directories.
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In the 'csrowX' directories are EDAC control and attribute files for
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this 'X' instance of csrow:
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@ -265,11 +232,11 @@ Total Correctable Errors count attribute file:
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'ce_count'
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This attribute file displays the total count of correctable
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errors that have occurred on this csrow. This
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count is very important to examine. CEs provide early
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indications that a DIMM is beginning to fail. This count
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field should be monitored for non-zero values and report
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such information to the system administrator.
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errors that have occurred on this csrow. This count is very
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important to examine. CEs provide early indications that a
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DIMM is beginning to fail. This count field should be
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monitored for non-zero values and report such information
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to the system administrator.
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Total memory managed by this csrow attribute file:
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@ -377,11 +344,13 @@ Channel 1 DIMM Label control file:
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motherboard specific and determination of this information
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must occur in userland at this time.
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============================================================================
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SYSTEM LOGGING
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If logging for UEs and CEs are enabled then system logs will have
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error notices indicating errors that have been detected:
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SYSTEM LOGGING
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--------------
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If logging for UEs and CEs is enabled, then system logs will contain
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information indicating that errors have been detected:
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EDAC MC0: CE page 0x283, offset 0xce0, grain 8, syndrome 0x6ec3, row 0,
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channel 1 "DIMM_B1": amd76x_edac
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@ -404,24 +373,23 @@ The structure of the message is:
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and then an optional, driver-specific message that may
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have additional information.
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Both UEs and CEs with no info will lack all but memory controller,
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error type, a notice of "no info" and then an optional,
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driver-specific error message.
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Both UEs and CEs with no info will lack all but memory controller, error
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type, a notice of "no info" and then an optional, driver-specific error
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message.
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============================================================================
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PCI Bus Parity Detection
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------------------------
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On Header Type 00 devices the primary status is looked at
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for any parity error regardless of whether Parity is enabled on the
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device. (The spec indicates parity is generated in some cases).
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On Header Type 01 bridges, the secondary status register is also
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looked at to see if parity occurred on the bus on the other side of
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the bridge.
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On Header Type 00 devices, the primary status is looked at for any
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parity error regardless of whether parity is enabled on the device or
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not. (The spec indicates parity is generated in some cases). On Header
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Type 01 bridges, the secondary status register is also looked at to see
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if parity occurred on the bus on the other side of the bridge.
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SYSFS CONFIGURATION
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-------------------
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Under /sys/devices/system/edac/pci are control and attribute files as follows:
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@ -450,8 +418,9 @@ Parity Count:
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have been detected.
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============================================================================
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MODULE PARAMETERS
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-----------------
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Panic on UE control file:
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@ -530,10 +499,8 @@ Panic on PCI PARITY Error:
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=======================================================================
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EDAC_DEVICE type of device
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EDAC device type
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----------------
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In the header file, edac_core.h, there is a series of edac_device structures
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and APIs for the EDAC_DEVICE.
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@ -573,6 +540,7 @@ The test_device_edac device adds at least one of its own custom control:
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The symlink points to the 'struct dev' that is registered for this edac_device.
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INSTANCES
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---------
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One or more instance directories are present. For the 'test_device_edac' case:
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@ -586,6 +554,7 @@ counter in deeper subdirectories.
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ue_count total of UE events of subdirectories
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BLOCKS
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------
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At the lowest directory level is the 'block' directory. There can be 0, 1
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or more blocks specified in each instance.
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@ -623,8 +592,9 @@ unique drivers for their hardware systems.
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The 'test_device_edac' sample driver is located at the
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bluesmoke.sourceforge.net project site for EDAC.
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=======================================================================
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NEHALEM USAGE OF EDAC APIs
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--------------------------
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This chapter documents some EXPERIMENTAL mappings for EDAC API to handle
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Nehalem EDAC driver. They will likely be changed on future versions
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@ -773,3 +743,20 @@ exports one
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by the driver. Since, with udimm, this is counted by software, it is
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possible that some errors could be lost. With rdimm's, they display the
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contents of the registers
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CREDITS:
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========
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Written by Doug Thompson <dougthompson@xmission.com>
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7 Dec 2005
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17 Jul 2007 Updated
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(c) Mauro Carvalho Chehab
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05 Aug 2009 Nehalem interface
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EDAC authors/maintainers:
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Doug Thompson, Dave Jiang, Dave Peterson et al,
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Mauro Carvalho Chehab
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Borislav Petkov
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||||
original author: Thayne Harbaugh
|
||||
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||||
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