linux-kernel - Re: [PATCH 2/8] driver-core: add asynchronous probing support for drivers

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Message-ID: <CAPcyv4gDEaBof-x_mUigayTv36MZrUMbkDbh0bzy0SbboePtHw@mail.gmail.com>
Date:	Wed, 8 Jul 2015 17:54:26 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...e.com>, Tom Gundersen <teg@...m.no>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Olof Johansson <olof@...om.net>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: [PATCH 2/8] driver-core: add asynchronous probing support for drivers

On Wed, Jul 8, 2015 at 5:52 PM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> On Wed, Jul 08, 2015 at 05:43:23PM -0700, Dan Williams wrote:
>> On Mon, Jul 6, 2015 at 4:38 PM, Dmitry Torokhov
>> <dmitry.torokhov@...il.com> wrote:
>> > On Sat, Jul 04, 2015 at 07:09:19AM -0700, Dan Williams wrote:
>> >> The problem I ran into was needing to remove devices that still had
>> >> yet to be probed and not being able to use registration completion vs
>> >> the device_lock() to effectively synchronize the sub-system.
>> >
>> > Why do you need to "synchronize the sub-system"? The asynchronous
>> > probing should be transparent to the driver. Just unregister the device
>> > (or the driver) and driver core will ensure that probe() is not in
>> > flight.
>>
>> Async registration is indeed transparent to the driver.  The primary
>> need to "flush registration" is the case of "region" devices that
>> reference a set of NVDIMM devices.  A region device requires all
>> related NVDIMMs to be active before the region can be enabled.
>
> Sounds like you need to call into the subsystem to let it know that the
> device is active and activate region devices when they are ready. Could
> be either explicit call or you can try using bus notifiers for
> bind/unbind events.
>
> BTW, do you handle bind/unbind via sysfs (everyone forgets about this
> mechanism)?

bind/unbind via systs is central to how libnvdimm operates.  It's
covered by our unit tests.
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