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

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Date:	Tue, 29 Mar 2016 15:11:35 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Darren Hart <dvhart@...radead.org>
Cc:	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	Pali Rohár <pali.rohar@...il.com>,
	"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>
Subject: Re: [PATCH v3] dell-rbtn: Ignore ACPI notifications if device is suspended

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