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    SubjectRe: [PATCH v2 00/20] libnd: non-volatile memory device support
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    On Tue, Apr 28, 2015 at 1:52 PM, Andy Lutomirski <luto@amacapital.net> wrote:
    > On Tue, Apr 28, 2015 at 11:24 AM, Dan Williams <dan.j.williams@intel.com> wrote:
    >> Changes since v1 [1]: Incorporates feedback received prior to April 24.
    >>
    >> 1/ Ingo said [2]:
    >>
    >> "So why on earth is this whole concept and the naming itself
    >> ('drivers/block/nd/' stands for 'NFIT Defined', apparently)
    >> revolving around a specific 'firmware' mindset and revolving
    >> around specific, weirdly named, overly complicated looking
    >> firmware interfaces that come with their own new weird
    >> glossary??"
    >>
    >> Indeed, we of course consulted the NFIT specification to determine
    >> the shape of the sub-system, but then let its terms and data
    >> structures permeate too deep into the implementation. That is fixed
    >> now with all NFIT specifics factored out into acpi.c. The NFIT is no
    >> longer required reading to review libnd. Only three concepts are
    >> needed:
    >>
    >> i/ PMEM - contiguous memory range where cpu stores are
    >> persistent once they are flushed through the memory
    >> controller.
    >>
    >> ii/ BLK - mmio apertures (sliding windows) that can be
    >> programmed to access an aperture's-worth of persistent
    >> media at a time.
    >>
    >> iii/ DPA - "dimm-physical-address", address space local to a
    >> dimm. A dimm may provide both PMEM-mode and BLK-mode
    >> access to a range of DPA. libnd manages allocation of DPA
    >> to either PMEM or BLK-namespaces to resolve this aliasing.
    >
    > Mostly for my understanding: is there a name for "address relative to
    > the address lines on the DIMM"? That is, a DIMM that exposes 8 GB of
    > apparent physical memory, possibly interleaved, broken up, or weirdly
    > remapped by the memory controller, would still have addresses between
    > 0 and 8 GB. Some of those might be PMEM windows, some might be MMIO,
    > some might be BLK apertures, etc.
    >
    > IIUC "DPA" refers to actual addressable storage, not this type of address?

    No, DPA is exactly as you describe above. You can't directly access
    it except through a PMEM mapping (possibly interleaved with DPA from
    other DIMMs) or a BLK aperture (mmio window into DPA).


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