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Subject[PATCH v2 23/24] EDAC, Documentation: Describe CPER module definition and DIMM ranks
Date
Update on CPER DIMM naming convention and DIMM ranks.

Signed-off-by: Robert Richter <rrichter@marvell.com>
---
Documentation/admin-guide/ras.rst | 31 +++++++++++++++++++------------
1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/Documentation/admin-guide/ras.rst b/Documentation/admin-guide/ras.rst
index c7495e42e6f4..4e2a01c77a9c 100644
--- a/Documentation/admin-guide/ras.rst
+++ b/Documentation/admin-guide/ras.rst
@@ -330,9 +330,12 @@ 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.
+ packaging alternatives, like SO-DIMM, SIMM, etc. The UEFI
+ specification (Version 2.7) defines a memory module in the Common
+ Platform Error Record (CPER) section to be an SMBIOS Memory Device
+ (Type 17). 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
@@ -349,12 +352,14 @@ controllers. The following example will assume 2 channels:
| | ``ch0`` | ``ch1`` |
+============+===========+===========+
| ``csrow0`` | DIMM_A0 | DIMM_B0 |
- +------------+ | |
- | ``csrow1`` | | |
+ | | rank0 | rank0 |
+ +------------+ - | - |
+ | ``csrow1`` | rank1 | rank1 |
+------------+-----------+-----------+
| ``csrow2`` | DIMM_A1 | DIMM_B1 |
- +------------+ | |
- | ``csrow3`` | | |
+ | | rank0 | rank0 |
+ +------------+ - | - |
+ | ``csrow3`` | rank1 | rank1 |
+------------+-----------+-----------+

In the above example, there are 4 physical slots on the motherboard
@@ -374,11 +379,13 @@ 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.
+In the example above 2 dual ranked DIMMs are similarly placed. Thus,
+both csrow0 and csrow1 are populated. On the other hand, when 2 single
+ranked DIMMs are placed in slots DIMM_A0 and DIMM_B0, then they will
+have just one csrow (csrow0) and csrow1 will be empty. The pattern
+repeats itself for csrow2 and csrow3. Also note that some memory
+controller doesn't have any logic to identify the memory module, see
+``rankX`` directories below.

The representation of the above is reflected in the directory
tree in EDAC's sysfs interface. Starting in directory
--
2.20.1
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