linux-kernel - Re: [PATCH v2 2/3] nfit, libnvdimm: allow an ARS scrub to be triggered on demand

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Message-ID: <CAPcyv4jEp6qrHUcBHoO2VmauacB7O5wZdnkZCXN-QYiXa=ecWg@mail.gmail.com>
Date:	Thu, 21 Jul 2016 12:59:37 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Linda Knippers <linda.knippers@....com>
Cc:	Vishal Verma <vishal.l.verma@...el.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	Tony Luck <tony.luck@...el.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] nfit, libnvdimm: allow an ARS scrub to be
 triggered on demand

On Thu, Jul 21, 2016 at 12:55 PM, Linda Knippers <linda.knippers@....com> wrote:
>
>
> On 7/21/2016 3:46 PM, Dan Williams wrote:
>> On Thu, Jul 21, 2016 at 12:40 PM, Linda Knippers <linda.knippers@....com> wrote:
>>> On 07/20/2016 09:50 PM, Vishal Verma wrote:
>>>> Normally, an ARS (Address Range Scrub) only happens at
>>>> boot/initialization time. There can however arise situations where a
>>>> bus-wide rescan is needed - notably, in the case of discovering a latent
>>>> media error, we should do a full rescan to figure out what other sectors
>>>> are bad, and thus potentially avoid triggering an mce on them in the
>>>> future. Also provide a sysfs trigger to start a bus-wide scrub.
>>>
>>> I don't see anything in here that checks to see if the platform actually
>>> supports ARS before setting all this stuff up.  Setting up an MCE handler
>>> and exposing a sysfs trigger for something that is optional and perhaps
>>> not implemented doesn't seem helpful.  Or is there a check that I missed?
>>
>> We'll get -ENOTTY to ars_start(), but you're right it's a good idea to
>> hide the scrub attribute if a platform does not have ars support.
>>
>> Vishal, can you add an is_visible() routine to
>> acpi_nfit_attribute_group() to hide 'scrub' on platforms that do not
>> implement the ARS commands?
>
> It's also possible that a platform might only support ARS at boot time
> so subsequent scrubs would fail or not return any new information.
> I don't think there's a way to know that in advice though.

I would hope a platform like that just marks the "ARS - Start" command
as not supported so that we don't even generate the failure.