linux-kernel - Re: [PATCH] Add support of NVDIMM memory error notification in ACPI 6.2

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Date:   Wed, 7 Jun 2017 21:33:31 +0000
From:   "Kani, Toshimitsu" <toshi.kani@....com>
To:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>
Subject: Re: [PATCH] Add support of NVDIMM memory error notification in ACPI
 6.2

On Wed, 2017-06-07 at 14:06 -0700, Dan Williams wrote:
> On Wed, Jun 7, 2017 at 1:57 PM, Kani, Toshimitsu <toshi.kani@....com>
> wrote:
> > On Wed, 2017-06-07 at 12:09 -0700, Dan Williams wrote:
> > > On Wed, Jun 7, 2017 at 11:49 AM, Toshi Kani <toshi.kani@....com>
> > > wrote:
> > 
> >  :
> > > > +
> > > > +static void acpi_nfit_uc_error_notify(struct device *dev,
> > > > acpi_handle handle)
> > > > +{
> > > > +       struct acpi_nfit_desc *acpi_desc =
> > > > dev_get_drvdata(dev);
> > > > +
> > > > +       acpi_nfit_ars_rescan(acpi_desc);
> > > 
> > > I wonder if we should gate re-scanning with a similar:
> > > 
> > >     if (acpi_desc->scrub_mode == HW_ERROR_SCRUB_ON)
> > > 
> > > ...check that we do in the mce notification case? Maybe not since
> > > we
> > > don't get an indication of where the error is without a rescan.
> > 
> > I think this mce case is different since the MCE handler already
> > knows where the new poison location is and can update badblocks
> > information for it.  Starting ARS is an optional precaution.
> > 
> > > However, at a minimum I think we need support for the new Start
> > > ARS flag ("If set to 1 the firmware shall return data from a
> > > previous scrub, if any, without starting a new scrub") and use
> > > that for this case.
> > 
> > That's an interesting idea.  But I wonder how users know if it is
> > OK to set this flag as it relies on BIOS implementation that is not
> > described in ACPI...
> 
> Ugh, you're right. We might need a revision-id=2 version of Start ARS
> so software knows that the BIOS is aware of the new flag.

My bad.  Looking at ACPI 6.2, it actually defines what you described. 
Start ARS now defines bit[1] in Flags which can be set to avoid
scanning for this notification.  I will update the patch to set this
flag when HW_ERROR_SCRUB_ON is not set.

Thanks,
-Toshi