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

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Date:	Thu, 21 Jul 2016 15:55:20 -0400
From:	Linda Knippers <linda.knippers@....com>
To:	Dan Williams <dan.j.williams@...el.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 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.

-- ljk