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

Andy Lutomirski
2015-04-28T21:06:15Z

On Tue, Apr 28, 2015 at 1:59 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> 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).

So the thing I'm describing has no name, then? Oh, well.

--Andy