Documentation/edac.txt: Improve it to reflect the latest changes at the driver

Signed-off-by: Mauro Carvalho Chehab <mcheahb@redhat.com>

Documentation/edac.txt

@@ -730,25 +730,41 @@ Due to the way Nehalem exports Memory Controller data, some adjustments
 were done at i7core_edac driver. This chapter will cover those differences
 
 1) On Nehalem, there are one Memory Controller per Quick Patch Interconnect
-   (QPI). At the driver, the term "socket" means one QPI. It should also be
-   associated with the CPU physical socket.
+   (QPI). At the driver, the term "socket" means one QPI. This is
+   associated with a physical CPU socket.
 
    Each MC have 3 physical read channels, 3 physical write channels and
    3 logic channels. The driver currenty sees it as just 3 channels.
    Each channel can have up to 3 DIMMs.
 
    The minimum known unity is DIMMs. There are no information about csrows.
-   As EDAC API maps the minimum unity is csrows, the driver exports one
+   As EDAC API maps the minimum unity is csrows, the driver sequencially
+   maps channel/dimm into different csrows.
+
+   For example, suposing the following layout:
+	Ch0 phy rd0, wr0 (0x063f4031): 2 ranks, UDIMMs
+	  dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
+	  dimm 1 1024 Mb offset: 4, bank: 8, rank: 1, row: 0x4000, col: 0x400
+        Ch1 phy rd1, wr1 (0x063f4031): 2 ranks, UDIMMs
+	  dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
+	Ch2 phy rd3, wr3 (0x063f4031): 2 ranks, UDIMMs
+	  dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
+   The driver will map it as:
+	csrow0: channel 0, dimm0
+	csrow1: channel 0, dimm1
+	csrow2: channel 1, dimm0
+	csrow3: channel 2, dimm0
+
+exports one
    DIMM per csrow.
 
-   Currently, it also exports the several memory controllers as just one. This
-   limit will be removed on future versions of the driver.
+   Each QPI is exported as a different memory controller.
 
 2) Nehalem MC has the hability to generate errors. The driver implements this
    functionality via some error injection nodes:
 
    For injecting a memory error, there are some sysfs nodes, under
-   /sys/devices/system/edac/mc/mc0/:
+   /sys/devices/system/edac/mc/mc?/:
 
    inject_addrmatch:
       Controls the error injection mask register. It is possible to specify
@@ -779,11 +795,6 @@ were done at i7core_edac driver. This chapter will cover those differences
 		2 for the highest
 		1 for the lowest
 
-   inject_socket:
-       specifies what QPI (or processor socket) will generate the error.
-          on Xeon 35xx, it should be 0.
-          on Xeon 55xx, it should be 0 or 1.
-
    inject_type:
        specifies the type of error, being a combination of the following bits:
 		bit 0 - repeat
@@ -806,10 +817,12 @@ were done at i7core_edac driver. This chapter will cover those differences
    echo 2 >/sys/devices/system/edac/mc/mc0/inject_type
    echo 64 >/sys/devices/system/edac/mc/mc0/inject_eccmask
    echo 3 >/sys/devices/system/edac/mc/mc0/inject_section
-   echo 0 >/sys/devices/system/edac/mc/mc0/inject_socket
    echo 1 >/sys/devices/system/edac/mc/mc0/inject_enable
    dd if=/dev/mem of=/dev/null seek=16k bs=4k count=1 >& /dev/null
 
+   For socket 1, it is needed to replace "mc0" by "mc1" at the above
+   commands.
+
    The generated error message will look like:
 
    EDAC MC0: UE row 0, channel-a= 0 channel-b= 0 labels "-": NON_FATAL (addr = 0x0075b980, socket=0, Dimm=0, Channel=2, syndrome=0x00000040, count=1, Err=8c0000400001009f:4000080482 (read error: read ECC error))
@@ -821,9 +834,36 @@ were done at i7core_edac driver. This chapter will cover those differences
    separate sysfs note were created to handle such counters.
 
    They can be read by looking at the contents of "corrected_error_counts"
-   counter:
+   counter. Due to hardware limits, the output is different on machines
+   with unregistered memories and machines with registered ones.
+
+   With unregistered memories, it outputs:
 
 	$ cat /sys/devices/system/edac/mc/mc0/corrected_error_counts
-	dimm0: 15866
-	dimm1: 0
-	dimm2: 27285
+	all channels UDIMM0: 0 UDIMM1: 0 UDIMM2: 0
+
+   What happens here is that errors on different csrows, but at the same
+   dimm number will increment the same counter.
+   So, in this memory mapping:
+	csrow0: channel 0, dimm0
+	csrow1: channel 0, dimm1
+	csrow2: channel 1, dimm0
+	csrow3: channel 2, dimm0
+   The hardware will increment UDIMM0 for an error at either csrow0, csrow2
+   or csrow3.
+
+   With registered memories, it outputs:
+
+	$cat /sys/devices/system/edac/mc/mc0/corrected_error_counts
+	channel 0 RDIMM0: 0 RDIMM1: 0 RDIMM2: 0
+	channel 1 RDIMM0: 0 RDIMM1: 0 RDIMM2: 0
+	channel 2 RDIMM0: 0 RDIMM1: 0 RDIMM2: 0
+
+   So, with registered memories, there's a direct map between a csrow and a
+   counter.
+
+4) Standard error counters
+
+   The standard error counters are generated when an mcelog error is received
+   by the driver. Since it is counted by software, it is possible that some
+   errors could be lost.