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

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Date:	Wed, 29 Apr 2015 12:28:05 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	linux-nvdimm <linux-nvdimm@...ts.01.org>,
	Boaz Harrosh <boaz@...xistor.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...com>, "H. Peter Anvin" <hpa@...or.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Christoph Hellwig <hch@....de>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v2 20/20] libnd, nd_acpi, nd_blk: driver for BLK-mode
 access persistent memory

On Wed, Apr 29, 2015 at 10:10 AM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Tue, Apr 28, 2015 at 4:06 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Tue, Apr 28, 2015 at 3:30 PM, Dan Williams <dan.j.williams@...el.com> wrote:
>>> On Tue, Apr 28, 2015 at 2:10 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>>> On Tue, Apr 28, 2015 at 11:26 AM, Dan Williams <dan.j.williams@...el.com> wrote:
>>>>> From: Ross Zwisler <ross.zwisler@...ux.intel.com>
>>>>>
>>>>> 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@...capital.net>
>>>>> Cc: Boaz Harrosh <boaz@...xistor.com>
>>>>> Cc: H. Peter Anvin <hpa@...or.com>
>>>>> Cc: Jens Axboe <axboe@...com>
>>>>> Cc: Ingo Molnar <mingo@...nel.org>
>>>>> Cc: Christoph Hellwig <hch@....de>
>>>>> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
>>>>> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
>>>>> ---
>>>>>  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.
>>
>> Right, I was assuming incorrectly that the sector-atomic thing was a
>> necessary part of BLK, or at least of this implementation.
>>
>> Anyway, I think my point stands: let's describe what these drivers do
>> from a user's perspective, not how they work.
>
> Agreed.  How about:
>
> "Support NVDIMMs, or other devices, that implement a BLK-mode access
> capability.  BLK-mode access uses memory-mapped-i/o apertures to
> access persistent media.
>
> Say Y if your platform firmware emits an ACPI.NFIT table
> (CONFIG_ND_ACPI), or otherwise exposes BLK-mode capabilities."

Sure.

--Andy
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