linux-kernel - Re: [PATCH 3/3] ACPI: Change NFIT driver to set PMEM type to iomem entry

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Date:	Fri, 12 Feb 2016 15:30:03 -0700
From:	Toshi Kani <toshi.kani@....com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] ACPI: Change NFIT driver to set PMEM type to iomem
 entry

On Fri, 2016-02-12 at 11:41 -0800, Dan Williams wrote:
> On Tue, Feb 2, 2016 at 10:55 AM, Toshi Kani <toshi.kani@....com> wrote:
> > Change acpi_nfit_register_region() to call iomem_set_desc() with
> > IORES_DESC_PERSISTENT_MEMORY for NFIT_SPA_PM ranges found in ACPI
> > NFIT table.
> > 
> > When FW sets E820_PMEM in e820 and EFI_PERSISTENT_MEMORY in EFI,
> > this code simply sets PMEM type again to "Persistent Memory" entries
> > in the iomem table.  When FW sets reserved type for persistent
> > memory ranges, it sets PMEM type to "reserved" entries covering
> > PMEM ranges.
> > 
> > This allows the EINJ driver, which calls region_intersects() with
> > IORES_DESC_PERSISTENT_MEMORY to check persistent memory ranges,
> > to work continuously even if FW sets reserved type to persistent
> > memory in e820 and EFI.
> > 
> > Signed-off-by: Toshi Kani <toshi.kani@....com>
> > Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Borislav Petkov <bp@...e.de>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> >  drivers/acpi/nfit.c |    6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/acpi/nfit.c b/drivers/acpi/nfit.c
> > index ad6d8c6..add04f0 100644
> > --- a/drivers/acpi/nfit.c
> > +++ b/drivers/acpi/nfit.c
> > @@ -1781,6 +1781,12 @@ static int acpi_nfit_register_region(struct
> > acpi_nfit_desc *acpi_desc,
> > 
> >         nvdimm_bus = acpi_desc->nvdimm_bus;
> >         if (nfit_spa_type(spa) == NFIT_SPA_PM) {
> > +               rc = iomem_set_desc(spa->address, spa->length,
> > +                                       IORES_DESC_PERSISTENT_MEMORY);
> > +               if (rc)
> > +                       dev_dbg(acpi_desc->dev,
> > +                               "error setting iomem desc: %d\n", rc);
> > +
> 
> Hmm, if we set the type on driver load, should we clear the type on
> driver unload?

I think this type update should stay for the life-cycle of this iomem entry
itself since this range is PMEM even after the driver is unloaded.  This is
an extension of the boot-time iomem table initialization from e820/EFI,
which allows ACPI to set a correct type.  This is independent from driver's
resource allocations.

> Actually it might be more straightforward to specify a type at
> request_region() time.  That way it gets released at release_region().
> We're already setting a resource name at request_region time, adding a
> type annotation at the time seems appropriate.

I first considered simply setting "namespaceX.X" as PMEM.  However,
region_intersects() and its friends only check the top-level entries, not
their children, of the iomem table.  And I think a child should have the
same type as the parent as I fixed it in patch 1/3.

Thanks,
-Toshi