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Subject[PATCH 6/6] drivers edac add to edac docs
From:	Doug Thompson <dougthompson@xmission.com>

Updated the EDAC kernel documentation

Signed-off-by: Doug Thompson <dougthompson@xmission.com>
---
edac.txt | 192 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 165 insertions(+), 27 deletions(-)

Index: linux-2.6.22-rc6-mm1/Documentation/drivers/edac/edac.txt
===================================================================
--- linux-2.6.22-rc6-mm1.orig/Documentation/drivers/edac/edac.txt
+++ linux-2.6.22-rc6-mm1/Documentation/drivers/edac/edac.txt
@@ -2,22 +2,42 @@

EDAC - Error Detection And Correction

-Written by Doug Thompson <norsk5@xmission.com>
+Written by Doug Thompson <dougthompson@xmission.com>
7 Dec 2005
+17 Jul 2007 Updated


-EDAC was written by:
- Thayne Harbaugh,
- modified by Dave Peterson, Doug Thompson, et al,
- from the bluesmoke.sourceforge.net project.
+EDAC is maintained and written by:

+ Doug Thompson, Dave Jiang, Dave Peterson et al,
+ original author: Thayne Harbaugh,
+
+Contact:
+ website: bluesmoke.sourceforge.net
+ mailing list: bluesmoke-devel@lists.sourceforge.net
+
+"bluesmoke" was the name for this device driver when it was "out-of-tree"
+and maintained at sourceforge.net. When it was pushed into 2.6.16 for the
+first time, it was renamed to 'EDAC'.
+
+The bluesmoke project at sourceforge.net is now utilized as a 'staging area'
+for EDAC development, before it is sent upstream to kernel.org
+
+At the bluesmoke/EDAC project site, is a series of quilt patches against
+recent kernels, stored in a SVN respository. For easier downloading, there
+is also a tarball snapshot available.

============================================================================
EDAC PURPOSE

The 'edac' kernel module goal is to detect and report errors that occur
-within the computer system. In the initial release, memory Correctable Errors
-(CE) and Uncorrectable Errors (UE) are the primary errors being harvested.
+within the computer system running under linux.
+
+MEMORY
+
+In the initial release, memory Correctable Errors (CE) and Uncorrectable
+Errors (UE) are the primary errors being harvested. These types of errors
+are harvested by the 'edac_mc' class of device.

Detecting CE events, then harvesting those events and reporting them,
CAN be a predictor of future UE events. With CE events, the system can
@@ -25,9 +45,27 @@ continue to operate, but with less safet
proactive part replacement of memory DIMMs exhibiting CEs can reduce
the likelihood of the dreaded UE events and system 'panics'.

+NON-MEMORY
+
+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 Bus Parity and SERR Errors are scanned for on PCI devices
in order to determine if errors are occurring on 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
@@ -35,11 +73,17 @@ the vendor should tie the parity status
to generate parity. Some vendors do not do this, and thus the parity bit
can "float" giving false positives.

-[There are patches in the kernel queue which will allow for storage of
-quirks of PCI devices reporting false parity positives. The 2.6.18
-kernel should have those patches included. When that becomes available,
-then EDAC will be patched to utilize that information to "skip" such
-devices.]
+In the kernel 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 scannining is skipped for that device. The attribute
+is:
+
+ broken_parity_status
+
+as is located in /sys/devices/pci<XXX>/0000:XX:YY.Z directorys for
+PCI devices.
+
+FUTURE HARDWARE SCANNING

EDAC will have future error detectors that will be integrated with
EDAC or added to it, in the following list:
@@ -57,13 +101,14 @@ and the like.
============================================================================
EDAC VERSIONING

-EDAC is composed of a "core" module (edac_mc.ko) and several Memory
+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 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.
+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
@@ -88,8 +133,9 @@ EDAC sysfs INTERFACE
EDAC presents a 'sysfs' interface for control, reporting and attribute
reporting purposes.

-EDAC lives in the /sys/devices/system/edac directory. Within this directory
-there currently reside 2 'edac' components:
+EDAC lives in the /sys/devices/system/edac directory.
+
+Within this directory there currently reside 2 'edac' components:

mc memory controller(s) system
pci PCI control and status system
@@ -188,7 +234,7 @@ In directory 'mc' are EDAC system overal

Panic on UE control file:

- 'panic_on_ue'
+ 'edac_mc_panic_on_ue'

An uncorrectable error will cause a machine panic. This is usually
desirable. It is a bad idea to continue when an uncorrectable error
@@ -199,12 +245,12 @@ Panic on UE control file:

LOAD TIME: module/kernel parameter: panic_on_ue=[0|1]

- RUN TIME: echo "1" >/sys/devices/system/edac/mc/panic_on_ue
+ RUN TIME: echo "1" >/sys/devices/system/edac/mc/edac_mc_panic_on_ue


Log UE control file:

- 'log_ue'
+ 'edac_mc_log_ue'

Generate kernel messages describing uncorrectable errors. These errors
are reported through the system message log system. UE statistics
@@ -212,12 +258,12 @@ Log UE control file:

LOAD TIME: module/kernel parameter: log_ue=[0|1]

- RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ue
+ RUN TIME: echo "1" >/sys/devices/system/edac/mc/edac_mc_log_ue


Log CE control file:

- 'log_ce'
+ 'edac_mc_log_ce'

Generate kernel messages describing correctable errors. These
errors are reported through the system message log system.
@@ -225,12 +271,12 @@ Log CE control file:

LOAD TIME: module/kernel parameter: log_ce=[0|1]

- RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ce
+ RUN TIME: echo "1" >/sys/devices/system/edac/mc/edac_mc_log_ce


Polling period control file:

- 'poll_msec'
+ 'edac_mc_poll_msec'

The time period, in milliseconds, for polling for error information.
Too small a value wastes resources. Too large a value might delay
@@ -241,7 +287,7 @@ Polling period control file:

LOAD TIME: module/kernel parameter: poll_msec=[0|1]

- RUN TIME: echo "1000" >/sys/devices/system/edac/mc/poll_msec
+ RUN TIME: echo "1000" >/sys/devices/system/edac/mc/edac_mc_poll_msec


============================================================================
@@ -587,3 +633,95 @@ Parity Count:


=======================================================================
+
+
+EDAC_DEVICE type of device
+
+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 bluesmoke.sourceforget.net website)
+installs itself as:
+
+ /sys/devices/systm/edac/test-instance
+
+in this directory are various controls, a symlink and one or more 'instance'
+directorys.
+
+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 any others to create their own
+unique drivers for their hardware systems.
+
+The 'test_device_edac' sample driver is located at the
+bluesmoke.sourceforge.net project site for EDAC.
+
-
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