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

From: Yasuaki Ishimatsu
Date: Mon Feb 25 2013 - 22:40:56 EST

2013/02/26 12:11, Rafael J. Wysocki wrote:
On Tuesday, February 26, 2013 11:02:56 AM Yasuaki Ishimatsu wrote:
2013/02/26 10:09, Toshi Kani wrote:
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@xxxxxxxxx>

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

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

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

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.

+static void acpi_scan_bus_device_check(acpi_handle handle, u32 ost_source)
+ struct acpi_device *device = NULL;
+ 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,
+ 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
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

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?

My application does not distinguish between ADD and ONLINE events
currently. But if the event is changed from ONLINE to ADD, I will
change my application.

KOBJ_ADD is emitted for every struct acpi_device being registered, including
container devices, by acpi_device_add_finalize(). Can your application listen
to those events?

Ah O.K. I understood. Even if the ONLINE event disappers, my application can get
ADD event from acpi_device_add_finalize(). Of course, I need to change my
If the ADD event of container device is notified after hot adding devices which
are contained into container device, there is no reason to leave ONLINE event.

Yasuaki Ishimatsu


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