drivers/edac: add to edac docs
Updated the EDAC kernel documentation Signed-off-by: Doug Thompson <dougthompson@xmission.com> Cc: Greg KH <greg@kroah.com> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>hifive-unleashed-5.1
Doug Thompson
Linus Torvalds
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EDAC - Error Detection And Correction
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Written by Doug Thompson <norsk5@xmission.com>
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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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EDAC was written by:
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Thayne Harbaugh,
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modified by Dave Peterson, Doug Thompson, et al,
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from the bluesmoke.sourceforge.net project.
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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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"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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At the bluesmoke/EDAC project site, is a series of quilt patches against
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recent kernels, stored in a SVN respository. 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. In the initial release, memory Correctable Errors
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(CE) and Uncorrectable Errors (UE) are the primary errors being harvested.
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within the computer system running under linux.
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MEMORY
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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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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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@ -25,9 +45,27 @@ 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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NON-MEMORY
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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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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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PCI BUS SCANNING
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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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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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with regards to Parity generation and reporting. The specification says
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@ -35,11 +73,17 @@ 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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[There are patches in the kernel queue which will allow for storage of
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quirks of PCI devices reporting false parity positives. The 2.6.18
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kernel should have those patches included. When that becomes available,
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then EDAC will be patched to utilize that information to "skip" such
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devices.]
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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 scannining is skipped for that device. The attribute
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is:
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broken_parity_status
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as is located in /sys/devices/pci<XXX>/0000:XX:YY.Z directorys 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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@ -57,13 +101,14 @@ and the like.
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============================================================================
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EDAC VERSIONING
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EDAC is composed of a "core" module (edac_mc.ko) and several Memory
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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 have individual versions that reflect current release
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level of their respective modules. Thus, to "report" on what version
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a system is running, one must report both the CORE's and the
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MC driver's versions.
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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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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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LOADING
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@ -88,8 +133,9 @@ EDAC sysfs INTERFACE
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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 lives in the /sys/devices/system/edac directory. Within this directory
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there currently reside 2 'edac' components:
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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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mc memory controller(s) system
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pci PCI control and status system
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@ -188,7 +234,7 @@ In directory 'mc' are EDAC system overall control and attribute files:
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Panic on UE control file:
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'panic_on_ue'
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'edac_mc_panic_on_ue'
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An uncorrectable error will cause a machine panic. This is usually
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desirable. It is a bad idea to continue when an uncorrectable error
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@ -199,12 +245,12 @@ Panic on UE control file:
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LOAD TIME: module/kernel parameter: panic_on_ue=[0|1]
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/panic_on_ue
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/edac_mc_panic_on_ue
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Log UE control file:
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'log_ue'
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'edac_mc_log_ue'
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Generate kernel messages describing uncorrectable errors. These errors
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are reported through the system message log system. UE statistics
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@ -212,12 +258,12 @@ Log UE control file:
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LOAD TIME: module/kernel parameter: log_ue=[0|1]
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ue
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/edac_mc_log_ue
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Log CE control file:
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'log_ce'
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'edac_mc_log_ce'
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Generate kernel messages describing correctable errors. These
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errors are reported through the system message log system.
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@ -225,12 +271,12 @@ Log CE control file:
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LOAD TIME: module/kernel parameter: log_ce=[0|1]
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ce
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/edac_mc_log_ce
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Polling period control file:
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'poll_msec'
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'edac_mc_poll_msec'
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The time period, in milliseconds, for polling for error information.
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Too small a value wastes resources. Too large a value might delay
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@ -241,7 +287,7 @@ Polling period control file:
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LOAD TIME: module/kernel parameter: poll_msec=[0|1]
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RUN TIME: echo "1000" >/sys/devices/system/edac/mc/poll_msec
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RUN TIME: echo "1000" >/sys/devices/system/edac/mc/edac_mc_poll_msec
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============================================================================
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@ -587,3 +633,95 @@ Parity Count:
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=======================================================================
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EDAC_DEVICE type of device
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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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User space access to an edac_device is through the sysfs interface.
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At the location /sys/devices/system/edac (sysfs) new edac_device devices will
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appear.
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There is a three level tree beneath the above 'edac' directory. For example,
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the 'test_device_edac' device (found at the bluesmoke.sourceforget.net website)
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installs itself as:
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/sys/devices/systm/edac/test-instance
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in this directory are various controls, a symlink and one or more 'instance'
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directorys.
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The standard default controls are:
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log_ce boolean to log CE events
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log_ue boolean to log UE events
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panic_on_ue boolean to 'panic' the system if an UE is encountered
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(default off, can be set true via startup script)
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poll_msec time period between POLL cycles for events
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The test_device_edac device adds at least one of its own custom control:
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test_bits which in the current test driver does nothing but
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show how it is installed. A ported driver can
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add one or more such controls and/or attributes
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for specific uses.
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One out-of-tree driver uses controls here to allow
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for ERROR INJECTION operations to hardware
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injection registers
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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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One or more instance directories are present. For the 'test_device_edac' case:
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test-instance0
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In this directory there are two default counter attributes, which are totals of
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counter in deeper subdirectories.
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ce_count total of CE events of subdirectories
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ue_count total of UE events of subdirectories
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BLOCKS
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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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test-block0
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In this directory the default attributes are:
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ce_count which is counter of CE events for this 'block'
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of hardware being monitored
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ue_count which is counter of UE events for this 'block'
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of hardware being monitored
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The 'test_device_edac' device adds 4 attributes and 1 control:
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test-block-bits-0 for every POLL cycle this counter
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is incremented
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test-block-bits-1 every 10 cycles, this counter is bumped once,
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and test-block-bits-0 is set to 0
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test-block-bits-2 every 100 cycles, this counter is bumped once,
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and test-block-bits-1 is set to 0
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test-block-bits-3 every 1000 cycles, this counter is bumped once,
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and test-block-bits-2 is set to 0
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reset-counters writing ANY thing to this control will
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reset all the above counters.
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Use of the 'test_device_edac' driver should any others to create their own
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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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