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

Dan Williams
2015-04-28T20:59:44Z

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).