[PATCH] EDAC: Add memory scrubbing controls API to core

This is an attempt of providing an interface for memory scrubbing control in
EDAC.

This patch modifies the EDAC Core to provide the Interface for memory
controller modules to implment.

The following things are still outstanding:

 - K8 is the first implemenation,

   The patch provide a method of configuring the K8 hardware memory scrubber
   via the 'mcX' sysfs directory.  There should be some fallback to a generic
   scrubber implemented in software if the hardware does not support
   scrubbing.

   Or .. the scrubbing sysfs entry should not be visible at all.

 - Only works with SDRAM, not cache,

   The K8 can scrub cache and l2cache also - but I think this is not so
   useful as the cache is busy all the time (one hopes).

   One would also expect that cache scrubbing requires hardware support.

 - Error Handling,

   I would like that errors are returned to the user in "terms of file
   system".

 - Presentation,

   I chose Bandwidth in Bytes/Second as a representation of the scrubbing
   rate for the following reasons:

   I like that the sysfs entries are sort-of textual, related to something
   that makes sense instead of magical values that must be looked up.

   "My People" wants "% main memory scrubbed per hour" others prefer "%
   memory bandwidth used" as representation, "bandwith used" makes it easy to
   calculate both versions in one-liner scripts.

   If one later wants to scrub cache, the scaling becomes wierd for K8
   changing from "blocks of 64 byte memory" to "blocks of 64 cache lines" to
   "blocks of 64 bit".  Using "bandwidth used" makes sense in all three cases,
   (I.M.O.  anyway ;-).

 - Discovery,

   There is no way to discover the possible settings and what they do
   without reading the code and the documentation.

   *I* do not know how to make that work in a practical way.

 - Bugs(??),

   other tools can set invalid values in the memory scrub control register,
   those will read back as '-1', requiring the user to reset the scrub rate.
   This is how *I* think it should be.

 - Afflicting other areas of code,

   I made changes to edac_mc.c and edac_mc.h which will show up globally -
   this is not nice, it would be better that the memory scrubbing fuctionality
   and interface could be entirely contained within the memory controller it
   applies to.

Frithiof Jensen

edac_mc.c and its .h file is a CORE helper module for EDAC
driver modules. This provides the abstraction for device specific
drivers. It is fine to modify this CORE to provide help for
new features of the the drivers

doug thompson

Signed-off-by: Frithiof Jensen <frithiof.jensen@ericson.com>
Signed-off-by: doug thompson <norsk5@xmission.com>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/Documentation/drivers/edac/edac.txt b/Documentation/drivers/edac/edac.txt
index 7b3d969d2964..3c5a9e4297b4 100644
--- a/Documentation/drivers/edac/edac.txt
+++ b/Documentation/drivers/edac/edac.txt
@@ -339,7 +339,21 @@ Device Symlink:
 
         'device'
 
-        Symlink to the memory controller device
+        Symlink to the memory controller device.
+
+Sdram memory scrubbing rate:
+
+        'sdram_scrub_rate'
+
+        Read/Write attribute file that controls memory scrubbing. The scrubbing
+        rate is set by writing a minimum bandwith in bytes/sec to the attribute
+        file. The rate will be translated to an internal value that gives at
+        least the specified rate.
+
+        Reading the file will return the actual scrubbing rate employed.
+
+        If configuration fails or memory scrubbing is not implemented, the value
+        of the attribute file will be -1.