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

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Message-ID: <1429720742.15952.30.camel@misato.fc.hp.com>
Date:	Wed, 22 Apr 2015 10:39:02 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-nvdimm] [PATCH 04/21] nd: create an 'nd_bus' from an
 'nfit_desc'

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.  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.

[1] http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf

Thanks,
-Toshi 


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