Re: [RESEND v2 3/4] doc/devicetree: Persistent memory region bindings

From: Oliver <oohall@gmail.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Device Tree <devicetree@vger.kernel.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: [RESEND v2 3/4] doc/devicetree: Persistent memory region bindings
Date: Thu, 5 Apr 2018 21:34:12 +1000	[thread overview]
Message-ID: <CAOSf1CHu4R-t8q-8fL6Dyk7myFR0gTfd6-0cxqtBVGZgYZWGAw@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4if4un9mgFon4ttjKDYEtHC_GP6VoxUENp7YNS50T3afA@mail.gmail.com>

On Thu, Apr 5, 2018 at 12:21 AM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Wed, Apr 4, 2018 at 7:04 AM, Oliver <oohall@gmail.com> wrote:
>> On Wed, Apr 4, 2018 at 10:07 PM, Balbir Singh <bsingharora@gmail.com> wrote:
>>> On Tue, 3 Apr 2018 10:37:51 -0700
>>> Dan Williams <dan.j.williams@intel.com> wrote:
>>>
>>>> On Tue, Apr 3, 2018 at 7:24 AM, Oliver O'Halloran <oohall@gmail.com> wrote:
>>>> > Add device-tree binding documentation for the nvdimm region driver.
>>>> >
>>>> > Cc: devicetree@vger.kernel.org
>>>> > Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
>>>> > ---
>>>> > v2: Changed name from nvdimm-region to pmem-region.
>>>> >     Cleaned up the example binding and fixed the overlapping regions.
>>>> >     Added support for multiple regions in a single reg.
>>>> > ---
>>>> >  .../devicetree/bindings/pmem/pmem-region.txt       | 80 ++++++++++++++++++++++
>>>> >  MAINTAINERS                                        |  1 +
>>>> >  2 files changed, 81 insertions(+)
>>>> >  create mode 100644 Documentation/devicetree/bindings/pmem/pmem-region.txt
>>>>
>>>> Device-tree folks, does this look, ok?
>>>>
>>>> Oliver, is there any concept of a management interface to the
>>>> device(s) backing these regions? libnvdimm calls these "nmem" devices
>>>> and support operations like health status and namespace label
>>>> management.
>>
>> It's something I'm planning on implementing as soon as someone gives
>> me some hardware that isn't hacked up lab crap. I'm posting this
>> version with just regions since people have been asking for something
>> in upstream even if it's not fully featured.
>>
>> Grumbling aside, the plan is to have separate drivers for the DIMM
>> type. Discovering DIMM devices happens via the normal discovery
>> mechanisms (e.g. an NVDIMM supporting the JEDEC interface is an I2C
>> device) and when binding to a specific DIMM device it registers a DIMM
>> descriptor structure and a ndctl implementation for that DIMM type
>> with of_pmem. When of_pmem binds to a region it can plug everything
>> into the region specific bus. There's a few details to work out, but I
>> think it's a reasonable approach.
>
> Yeah, that sounds reasonable. It would mean that your management
> interface would need to understand that nmems on different buses could
> potentially move to another bus after a reconfiguration, but that's
> not too much different than the ACPI case where nmems can join and
> leave regions after a reset / reconfig.
>
>>> We would need a way to have nmem and pmem-regions find each other. Since we
>>> don't have the ACPI abstractions, the nmem region would need to add the
>>> ability for a driver to have a phandle to the interleaving and nmem properties.
>>>
>>> I guess that would be a separate driver, that would manage the nmem devices
>>> and there would be a way to relate the pmem and nmems. Oliver?
>>
>> Yes, that's the plan.
>
> So Balbir, is that enough for an Acked-by for this device-tree proposal?

For context Balbir is working with me on some of the pmem stuff. You
probably want an Ack from Rob rather than one of us.
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