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

On Wed, 4 Apr 2018 07:21:32 -0700
Dan Williams [off-list ref] wrote:

On Wed, Apr 4, 2018 at 7:04 AM, Oliver [off-list ref] wrote:

quoted

On Wed, Apr 4, 2018 at 10:07 PM, Balbir Singh [off-list ref] wrote:  

quoted

On Tue, 3 Apr 2018 10:37:51 -0700
Dan Williams [off-list ref] wrote:
 

quoted

On Tue, Apr 3, 2018 at 7:24 AM, Oliver O'Halloran [off-list ref] wrote:  

quoted

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.

quoted

quoted

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?

I don't see any major problems with the binding, but I think Oliver wanted
to send in a few clarifications based on a private discussion.

Balbir Singh.