What it is pointed by a csrow/channel vector is a rank information, and
not a channel information.
On a traditional architecture, the memory controller directly access the
memory ranks, via chip select rows. Different ranks at the same DIMM is
selected via different chip select rows. So, typically, one
csrow/channel pair means one different DIMM.
On FB-DIMMs, there's a microcontroller chip at the DIMM, called Advanced
Memory Buffer (AMB) that serves as the interface between the memory
controller and the memory chips.
The AMB selection is via the DIMM slot, and not via a csrow.
It is up to the AMB to talk with the csrows of the DRAM chips.
So, the FB-DIMM memory controllers see the DIMM slot, and not the DIMM
rank. RAMBUS is similar.
Newer memory controllers, like the ones found on Intel Sandy Bridge and
Nehalem, even working with normal DDR3 DIMM's, don't use the usual
channel A/channel B interleaving schema to provide 128 bits data access.
Instead, they have more channels (3 or 4 channels), and they can use
several interleaving schemas. Such memory controllers see the DIMMs
directly on their registers, instead of the ranks, which is better for
the driver, as its main usageis to point to a broken DIMM stick (the
Field Repleceable Unit), and not to point to a broken DRAM chip.
The drivers that support such such newer memory architecture models
currently need to fake information and to abuse on EDAC structures, as
the subsystem was conceived with the idea that the csrow would always be
visible by the CPU.
To make things a little worse, those drivers don't currently fake
csrows/channels on a consistent way, as the concepts there don't apply
to the memory controllers they're talking with. So, each driver author
interpreted the concepts using a different logic.
In order to fix it, let's rename the data structure that points into a
DIMM rank to "rank_info", in order to be clearer about what's stored
there.
Latter patches will provide a better way to represent the memory
hierarchy for the other types of memory controller.
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
a4b4be3fd7