linux-kernel - Re: [PATCH] i2c: allow specifying separate wakeup interrupt in device tree

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Date:	Mon, 24 Aug 2015 14:33:52 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Vignesh R <vigneshr@...com>, Tony Lindgren <tony@...mide.com>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Linux I2C <linux-i2c@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: allow specifying separate wakeup interrupt in
 device tree


> > When reviewing V2, I wasn't comfortable with just guessing what the old
> > code means. So, I did some digging and found:
> >
> > https://lkml.org/lkml/2008/8/10/204
> >
> > Quoting the interesting paragraph from David Brownell:
> >
> > ===
> >
> > Better would be to preserve any existing settings:
> >
> >         if (!device_can_wakeup(&client->dev))
> >                 device_init_wakeup(...)
> > That way the userspace policy setting is preserved unless the
> > device itself gets removed ... instead of being clobbered by
> > the simple act of (re)probing a driver.
> >
> >> > +   device_init_wakeup(&client->dev, client->flags &
> >> > I2C_CLIENT_WAKE);
> >
> > ===
> >
> > I have to admit that I am not familiar with device wakeup handling and
> > especially its userspace policies. Can you double check that your V2
> > meets the above intention?
> 
> No it does not; it explicitly resets the wakeup flag. Note that the
> original code was not quite right in that regard either: it would
> preserve wakeup flag set by userspace upon driver rebinding; but it
> would re-arm the wakeup flag if it was disabled by userspace.
> 
> I believe that resetting the flag upon re-binding the driver is proper
> behavior as the driver is responsible for setting up and handling
> wakeups.

Okay, that meets my idea of how this should work. I rephrased the above
paragraph slightly and added it to the commit message of V2.

Thanks,

   Wolfram


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