linux-kernel - Re: [PATCH v3] dell-rbtn: Ignore ACPI notifications if device is suspended

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Date:	Mon, 25 Apr 2016 22:06:11 +0200
From:	Gabriele Mazzotta <gabriele.mzt@...il.com>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Darren Hart <dvhart@...radead.org>,
	"D. Jared Dominguez" <Jared_Dominguez@...l.com>,
	"platform-driver-x86@...r.kernel.org" 
	<platform-driver-x86@...r.kernel.org>,
	Alex Hung <alex.hung@...onical.com>,
	Andrei Borzenkov <arvidjaar@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v3] dell-rbtn: Ignore ACPI notifications if device is suspended

2016-04-18 14:35 GMT+02:00 Pali Rohár <pali.rohar@...il.com>:
> On Tuesday 29 March 2016 15:11:35 Rafael J. Wysocki wrote:
>> On Monday, March 28, 2016 10:33:09 AM Darren Hart wrote:
>> > On Thu, Mar 24, 2016 at 12:24:56PM +0100, Gabriele Mazzotta wrote:
>> > > 2016-03-24 10:39 GMT+01:00 Pali Rohár <pali.rohar@...il.com>:
>> > > > On Monday 21 March 2016 16:13:34 Gabriele Mazzotta wrote:
>> > > >> 2016-03-21 13:17 GMT+01:00 Pali Rohár <pali.rohar@...il.com>:
>> > > >> > On Friday 18 March 2016 23:44:23 Gabriele Mazzotta wrote:
>> > > >> >> +#ifdef CONFIG_PM_SLEEP
>> > > >> >> +static void ACPI_SYSTEM_XFACE rbtn_acpi_clear_flag(void *context)
>> > > >> >> +{
>> > > >> >> +     struct rbtn_data *rbtn_data = context;
>> > > >> >> +
>> > > >> >> +     rbtn_data->suspended = false;
>> > > >> >> +}
>> > > >> >> +
>> > > >> >> +static int rbtn_suspend(struct device *dev)
>> > > >> >> +{
>> > > >> >> +     struct acpi_device *device = to_acpi_device(dev);
>> > > >> >> +     struct rbtn_data *rbtn_data = acpi_driver_data(device);
>> > > >> >> +
>> > > >> >> +     rbtn_data->suspended = true;
>> > > >> >> +
>> > > >> >> +     return 0;
>> > > >> >> +}
>> > > >> >> +
>> > > >> >> +static int rbtn_resume(struct device *dev)
>> > > >> >> +{
>> > > >> >> +     struct acpi_device *device = to_acpi_device(dev);
>> > > >> >> +     struct rbtn_data *rbtn_data = acpi_driver_data(device);
>> > > >> >> +     acpi_status status;
>> > > >> >> +
>> > > >> >> +     /*
>> > > >> >> +      * Clear the flag only after we received the extra
>> > > >> >> +      * ACPI notification.
>> > > >> >> +      */
>> > > >> >> +     status = acpi_os_execute(OSL_NOTIFY_HANDLER,
>> > > >> >> +                      rbtn_acpi_clear_flag, rbtn_data);
>> > > >> >> +     if (ACPI_FAILURE(status))
>> > > >> >> +             rbtn_data->suspended = false;
>> > > >> >
>> > > >> > I case when acpi_os_execute success it calls rbtn_acpi_clear_flag,
>> > > >> > right? And that will set suspended to false. When acpi_os_execute fails,
>> > > >> > then it set suspended too to false... Then whole acpi_os_execute doing
>> > > >> > just "barrier" after which suspended flag can be set to false. So I
>> > > >> > think rbtn_acpi_clear_flag function is not needed here.
>> > > >> >
>> > > >> > Cannot you pass NULL or empty function pointer as callback? Or what was
>> > > >> > reason to do that flag clearing at "two places"?
>> > > >>
>> > > >> acpi_os_execute doesn't wait for the callback to be executed, so
>> > > >> I can't clear the flag from rbtn_resume.
>> > > >
>> > > > acpi_os_execute calls callback asynchronously later? Or what exactly do it?
>> > >
>> > > In this case, it adds the callback to the kacpi_notify_wq workqueue
>> > > for deferred execution.
>> >
>> > +Rafael for context/advice on the use of acpi_os_execute here.
>> >
>> > This is true, but a quick scan through that call path doesn't tell me why we
>> > would need to call it here instead of just setting rbtn_data->suspended = false.
>> > The comment suggests waiting for the event, but is that what this is doing? It
>> > appears to me to be immediately scheduling the function to a work queue, not
>> > waiting for the event notifier.
>>
>> I think this is supposed to work as a barrier.  That is, it will only run after
>> all events in the queue have been processed.
>>
>> I'm not sure if that's necessary, though.
>>
>> Thanks,
>> Rafael
>>
>
> Darren, Gabriele, what is state of this patch? Bug is not still fixed,
> right?

Yes, the bug is still there and this patch fixes it.

Just to make it clear, we need the barrier. Andrei could reproduce
the bug without it [1], but not with it, as he confirmed in this
thread [2].

[1] http://article.gmane.org/gmane.linux.drivers.platform.x86.devel/8001
[2] http://article.gmane.org/gmane.linux.drivers.platform.x86.devel/8937

> --
> Pali Rohár
> pali.rohar@...il.com