Re: [PATCH v2 00/20] libnd: non-volatile memory device support

[Dan Williams]

On Tue, Apr 28, 2015 at 2:06 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Tue, Apr 28, 2015 at 1:59 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>> On Tue, Apr 28, 2015 at 1:52 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>>> On Tue, Apr 28, 2015 at 11:24 AM, Dan Williams <dan.j.williams@xxxxxxxxx> 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).
>
> So the thing I'm describing has no name, then?  Oh, well.

What?  The thing you are describing *is* DPA.
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