linux-kernel - Re: [Linux-nvdimm] [PATCH 04/21] nd: create an 'nd_bus' from an 'nfit

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Date:	Wed, 22 Apr 2015 12:28:17 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Toshi Kani <toshi.kani@...com>
Cc:	Linda Knippers <linda.knippers@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [Linux-nvdimm] [PATCH 04/21] nd: create an 'nd_bus' from an 'nfit_desc'

On Wed, Apr 22, 2015 at 11:23 AM, Toshi Kani <toshi.kani@...com> wrote:
> On Wed, 2015-04-22 at 11:20 -0700, Dan Williams wrote:
>> On Wed, Apr 22, 2015 at 11:00 AM, Linda Knippers <linda.knippers@...com> wrote:
>> Wait, point of clarification, DCRs (dimm-control-regions) have RFICs,
>> not MEMDEVs (memory-device-to-spa-mapping).  Toshi's original report
>> was that an NFIT with a SPA+MEMDEV was failing to enable a PMEM
>> device.  That specific problem can be fixed by either deleting the
>> MEMDEV, or adding a DCR.
>
> By a DCR, do you mean a DCR structure or SPA with Control Region GUID?

Hmm, I meant a DCR as defined below.  I agree you would not need a "SPA-DCR".

> Adding a DCR structure does not solve this issue since it requires SPA
> with Control Region GUID, which battery-backed DIMMs do not have.

I would not go that far, half of a DCR entry is relevant for any
NVDIMM, and half is only relevant if a DIMM offers BLK access:

struct acpi_nfit_dcr {
        u16 type;
        u16 length;
        u16 dcr_index;
        u16 vendor_id;
        u16 device_id;
        u16 revision_id;
        u16 sub_vendor_id;
        u16 sub_device_id;
        u16 sub_revision_id;
        u8 reserved[6];
        u32 serial_number;
        u16 fic;
<<<<< BLK relevant fields start here <<<<<
        u16 num_bcw;
        u64 bcw_size;
        u64 cmd_offset;
        u64 cmd_size;
        u64 status_offset;
        u64 status_size;
        u16 flags;
        u8 reserved2[6];
};

>> Of course, if you add a DCR with a different intended DSM layout than
>> the DSM-example-interface the driver will need to add support for
>> handling that case.
>
> Yes, we consider to add different _DSMs for management.  We do not need
> the nd_acpi driver to support it now, but we need this framework to work
> without the DSM-example-interface present.
>

One possible workaround is that I could ignore MEMDEV entries that do
not have a corresponding DCR.  This would enable nd_namespace_io
devices to be surfaced for your use case.  Would that work for you?
I.e. do you need the nfit_handle exposed?
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