linux-kernel - Re: [Update 4][PATCH 2/7] ACPI / scan: Introduce common code for ACPI-based device hotplug

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Date:	Mon, 25 Feb 2013 18:09:02 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	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>, 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 09:40 +0900, Yasuaki Ishimatsu wrote:
> 2013/02/26 8:39, 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.
> 
> My system expects this event to be notified when hot adding container device.
> My container device has cpu and memory. As Toshi said, these devices are
> offline when hot adding container device. So in my system, when notifying
> container device's KOBJ_ONLINE event, my application runs for onlining these
> devices. If this event is not notified to user land, we cannot online these
> devices  automatically.

Thanks for the info.  Can your application listen KOBJ_ADD to a
container device, instead of KOBJ_ONLINE?  IOW, does it distinguish
between ADD and ONLINE events to a container device?

-Toshi


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