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 11:07:52 -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 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.  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%.

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.

Thanks,
-Toshi

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