Re: [PATCH v2 20/20] libnd, nd_acpi, nd_blk: driver for BLK-mode access persistent memory

From: Dan Williams
Date: Tue Apr 28 2015 - 18:30:27 EST


On Tue, Apr 28, 2015 at 2:10 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Tue, Apr 28, 2015 at 11:26 AM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>> From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
>>
>> The libnd implementation handles allocating dimm address space (DPA)
>> between PMEM and BLK mode interfaces. After DPA has been allocated from
>> a BLK-region to a BLK-namespace the nd_blk driver attaches to handle I/O
>> as a struct bio based block device. Unlike PMEM, BLK is required to
>> handle platform specific details like mmio register formats and memory
>> controller interleave. For this reason the libnd generic nd_blk driver
>> calls back into the bus provider to carry out the I/O.
>>
>> This initial implementation handles the BLK interface defined by the
>> ACPI 6 NFIT [1] and the NVDIMM DSM Interface Example [2] composed from
>> DCR (dimm control region), BDW (block data window), IDT (interleave
>> descriptor) NFIT structures and the hardware register format.
>> [1]: http://www.uefi.org/sites/default/files/resources/ACPI_6.0.pdf
>> [2]: http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf
>>
>> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>> Cc: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
>> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
>> Cc: Jens Axboe <axboe@xxxxxx>
>> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>> Cc: Christoph Hellwig <hch@xxxxxx>
>> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
>> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>> ---
>> drivers/block/nd/Kconfig | 12 +
>> drivers/block/nd/Makefile | 3
>> drivers/block/nd/acpi.c | 422 +++++++++++++++++++++++++++++++++++--
>> drivers/block/nd/acpi_nfit.h | 47 ++++
>> drivers/block/nd/blk.c | 264 +++++++++++++++++++++++
>> drivers/block/nd/libnd.h | 11 +
>> drivers/block/nd/namespace_devs.c | 47 ++++
>> drivers/block/nd/nd-private.h | 3
>> drivers/block/nd/nd.h | 16 +
>> drivers/block/nd/region.c | 8 +
>> drivers/block/nd/region_devs.c | 65 +++++-
>> drivers/block/nd/test/nfit.c | 29 +++
>> drivers/block/nd/test/nfit_test.h | 2
>> 13 files changed, 891 insertions(+), 38 deletions(-)
>> create mode 100644 drivers/block/nd/blk.c
>>
>> diff --git a/drivers/block/nd/Kconfig b/drivers/block/nd/Kconfig
>> index 612bf2b14283..bac4290129fc 100644
>> --- a/drivers/block/nd/Kconfig
>> +++ b/drivers/block/nd/Kconfig
>> @@ -95,6 +95,18 @@ config BLK_DEV_PMEM
>>
>> Say Y if you want to use a NVDIMM described by ACPI, E820, etc...
>>
>> +config ND_BLK
>> + tristate "BLK: Block data window (aperture) device support"
>> + depends on LIBND
>> + default ND_ACPI
>> + help
>> + This driver performs I/O using a set of mmio windows on a
>> + dimm. The set of apertures will all access the one DIMM.
>> + Multiple windows allow multiple threads to have a different
>> + portions of the dimm open at one time.
>> +
>> + Say Y if you want to use a NVDIMM with BLK-mode capability
>> +
>
> This describes how it works, not what it is. How about:
>
> This driver exposes NVDIMM BLK regions as block devices. BLK regions
> are regions of NVDIMM storage that are sector-addressable, not
> byte-addressible, and do not support DAX.

They *are* byte-addressable albeit through an indirection window. The
indirection windows are too small for DAX to be a viable access mode.
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