Date:	Wed, 22 Apr 2015 14:00:57 -0400
From:	Linda Knippers <linda.knippers@...com>
To:	Dan Williams <dan.j.williams@...el.com>,
	Toshi Kani <toshi.kani@...com>
CC:	"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 4/22/2015 1:03 PM, Dan Williams wrote:
> On Wed, Apr 22, 2015 at 9:39 AM, Toshi Kani <toshi.kani@...com> wrote:
>> On Tue, 2015-04-21 at 13:35 -0700, Dan Williams wrote:
>>> On Tue, Apr 21, 2015 at 12:55 PM, Toshi Kani <toshi.kani@...com> wrote:
>>>> On Tue, 2015-04-21 at 12:58 -0700, Dan Williams wrote:
>>>>> On Tue, Apr 21, 2015 at 12:35 PM, Toshi Kani <toshi.kani@...com> wrote:
>>>>>> On Fri, 2015-04-17 at 21:35 -0400, Dan Williams wrote:
>>>>>>  :
>>>>>>> +
>>>>>>> +static int nd_mem_init(struct nd_bus *nd_bus)
>>>>>>> +{
>>>>>>> +     struct nd_spa *nd_spa;
>>>>>>> +
>>>>>>> +     /*
>>>>>>> +      * For each SPA-DCR address range find its corresponding
>>>>>>> +      * MEMDEV(s).  From each MEMDEV find the corresponding DCR.
>>>>>>> +      * Then, try to find a SPA-BDW and a corresponding BDW that
>>>>>>> +      * references the DCR.  Throw it all into an nd_mem object.
>>>>>>> +      * Note, that BDWs are optional.
>>>>>>> +      */
>>>>>>> +     list_for_each_entry(nd_spa, &nd_bus->spas, list) {
>>>>>>> +             u16 spa_index = readw(&nd_spa->nfit_spa->spa_index);
>>>>>>> +             int type = nfit_spa_type(nd_spa->nfit_spa);
>>>>>>> +             struct nd_mem *nd_mem, *found;
>>>>>>> +             struct nd_memdev *nd_memdev;
>>>>>>> +             u16 dcr_index;
>>>>>>> +
>>>>>>> +             if (type != NFIT_SPA_DCR)
>>>>>>> +                     continue;
>>>>>>
>>>>>> This function requires NFIT_SPA_DCR, SPA Range Structure with NVDIMM
>>>>>> Control Region GUID, for initializing an nd_mem object.  However,
>>>>>> battery-backed DIMMs do not have such control region SPA.  IIUC, the
>>>>>> NFIT spec does not require NFIT_SPA_DCR.
>>>>>>
>>>>>> Can you change this function to work with NFIT_SPA_PM as well?
>>>>>
>>>>> NFIT_SPA_PM ranges are handled separately from nd_mem_init().  See
>>>>> nd_region_create() in patch 10.
>>>>
>>>> If nd_mem_init() does not initialize nd_mem objects, nd_bus_probe() in
>>>> core.c fails in nd_bus_init_interleave_sets() and skips all subsequent
>>>> nd_bus_xxx() calls.  So, nd_region_create() won't be called.
>>>>
>>>> nd_bus_init_interleave_sets() fails because init_interleave_set()
>>>> returns -ENODEV if (!nd_mem).
>>>
>>> Ah, ok  your test case is specifying PMEM backed by memory device
>>> info.  We have a test case for simple ranges (nfit_test1_setup()), but
>>> it doesn't hit this bug because it does not specify any memory-device
>>> tables.
>>
>> Yes, we have NFIT table with SPA range (PM), memory device to SPA, and
>> NVDIMM control region structures.  With the memory device to SPA
>> structure, this code requires full sets of information, including the
>> namespace label data in _DSM [1], which is outside of ACPI 6.0 and is
>> optional.  Battery-backed DIMMs do not have such label data.
> 
> This is what "nd_namespace_io" devices are for, they do not require labels.
> 
> Question, if you don't have labels and you don't have DSMs then why
> publish a MEMDEV table at all?  Why not simply publish an anonymous
> range?  See nfit_test1_setup().

The MEMDEV table provides useful information, and there may be _DSMs,
perhaps just not the same _DSM as some other devices.

>> It needs
>> to work with NFIT table with these structures without this _DSM or with
>> a different type of _DSM which this code may or may not need to support.
>> It should also check Region Format Interface Code (RFIC) in the NVDIMM
>> control region structure before assuming this _DSM is present to
>> implement RFIC 0x0201.
> 
> Ok I can look into adding this check, but I don't think it is
> necessary if you simply refrain from publishing a MEMDEV entry.

But we need the MEMDEV. And as Toshi mentions, we could have other
RFICs with other _DSMs than your example.  That's why there is an RFIC.

-- ljk


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