Date:	Mon, 25 Feb 2013 16:32:24 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Jiang Liu <liuj97@...il.com>
Subject: Re: [Update 4][PATCH 2/7] ACPI / scan: Introduce common code for
 ACPI-based device hotplug

On Tue, 2013-02-26 at 00:39 +0100, Rafael J. Wysocki wrote:
> On Monday, February 25, 2013 11:07:52 AM Toshi Kani wrote:
> > On Sat, 2013-02-23 at 22:38 +0000, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > 
> > > Multiple drivers handling hotplug-capable ACPI device nodes install
> > > notify handlers covering the same types of events in a very similar
> > > way.  Moreover, those handlers are installed in separate namespace
> > > walks, although that really should be done during namespace scans
> > > carried out by acpi_bus_scan().  This leads to substantial code
> > > duplication, unnecessary overhead and behavior that is hard to
> > > follow.
> > > 
> > > For this reason, introduce common code in drivers/acpi/scan.c for
> > > handling hotplug-related notification and carrying out device
> > > insertion and eject operations in a generic fashion, such that it
> > > may be used by all of the relevant drivers in the future.  To cover
> > > the existing differences between those drivers introduce struct
> > > acpi_hotplug_profile for representing collections of hotplug
> > > settings associated with different ACPI scan handlers that can be
> > > used by the drivers to make the common code reflect their current
> > > behavior.
> > > 
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > ---
> > > 
> > > This update causes acpi_bus_device_eject() to only emit KOBJ_OFFLINE uevent if
> > > autoexec is unset for the given scan handler.
> > > 
> > > This will require the doc in patch [5/7] to be updated which I'm going to do if
> > > everyone is OK with the $subject patch.
> > > 
> > > Thanks,
> > > Rafael
> >  :
> > > +
> > > +static void acpi_scan_bus_device_check(acpi_handle handle, u32 ost_source)
> > > +{
> > > +	struct acpi_device *device = NULL;
> > > +	u32 ost_code = ACPI_OST_SC_NON_SPECIFIC_FAILURE;
> > > +	int error;
> > > +
> > > +	mutex_lock(&acpi_scan_lock);
> > > +
> > > +	acpi_bus_get_device(handle, &device);
> > > +	if (device) {
> > > +		dev_warn(&device->dev, "Attempt to re-insert\n");
> > > +		goto out;
> > > +	}
> > > +	acpi_evaluate_hotplug_ost(handle, ost_source,
> > > +				  ACPI_OST_SC_INSERT_IN_PROGRESS, NULL);
> > > +	error = acpi_bus_scan(handle);
> > > +	if (error) {
> > > +		acpi_handle_warn(handle, "Namespace scan failure\n");
> > > +		goto out;
> > > +	}
> > > +	error = acpi_bus_get_device(handle, &device);
> > > +	if (error) {
> > > +		acpi_handle_warn(handle, "Missing device node object\n");
> > > +		goto out;
> > > +	}
> > > +	ost_code = ACPI_OST_SC_SUCCESS;
> > > +	if (device->handler && device->handler->hotplug.uevents)
> > > +		kobject_uevent(&device->dev.kobj, KOBJ_ONLINE);
> > 
> > I confirmed that the uevent crash issue was solved.  Thinking further, I
> > wonder if we need to emit KOBJ_ONLINE here.  This behavior is asymmetric
> > since we do not emit KOBJ_OFFLINE when autoeject is set.
> 
> Well, I put that in there only to be able to make the container driver behave
> in a backwards compatible way (which is to emit KOBJ_ONLINE at this point).
> 
> If the container driver doesn't need to emit KOBJ_ONLINE at all, I agree with
> your suggestion.
> 
> > The definition of ONLINE/OFFLINE event to an ACPI device object seems also
> > bogus since there is no online/offline operation to the ACPI device object
> > itself.
> > Online/offline operation is only possible to actual device, such as
> > system/cpu/cpu% and system/memory/memory%.
> 
> That's correct, but I don't know what the user space expectations are
> currently.

I see.  I agree that we should keep backward compatibility with this
patchset.

> > So, I'd suggest the following changes.
> >  - Remove the "uevents" attribute.  KOBJ_ONLINE/OFFLINE are not used for
> > ACPI device objects.
> >  - Make the !autoeject case as an exception for now, and emit
> > KOBJ_OFFLINE as a way to request off-lining to user.  This uevent is
> > tied with the !autoeject case.  We can then revisit if this use-case
> > needs to be supported going forward.  If so, we may want to consider a
> > different event type.
> 
> Well, what about avoiding to expose uevents and autoeject for now and
> exposing enabled only?  Drivers would still be able to set the other flags on
> init on init to enforce the backwards-compatible behavior.
> 
> I agree that it would be sufficient to use one additional flag then, to start
> with, but its meaning would be something like "keep backwards compatibility
> with the old container driver", so perhaps "autoeject" is not a good name.
> 
> What about "user_eject" (that won't be exposed to user space) instead?  Where,
> if set, it would meand "do not autoeject and emit KOBJ_OFFLINE/ONLINE uevents
> like the old container driver did"?

Good idea!

Thanks,
-Toshi


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