linux-kernel - Re: [PATCH v4] gpio: lib-sysfs: Add 'wakeup' attribute

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Message-ID: <bb967ff02726449ab6525d33bccde7e4@BL2FFO11FD014.protection.gbl>
Date:	Thu, 29 Jan 2015 09:23:14 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Alexandre Courbot <gnurou@...il.com>,
	Johan Hovold <johan@...nel.org>, <linux-api@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v4] gpio: lib-sysfs: Add 'wakeup' attribute

Hi Linus,

On Mon, 2015-01-19 at 09:54AM +0100, Linus Walleij wrote:
> On Mon, Jan 19, 2015 at 5:20 AM, Alexandre Courbot <gnurou@...il.com> wrote:
> > On Sat, Jan 17, 2015 at 1:49 AM, Sören Brinkmann <soren.brinkmann@...inx.com> wrote:
> >> On Fri, 2015-01-16 at 12:11PM +0100, Johan Hovold wrote:
> 
> >>> Implementing proper wakeup support for unclaimed GPIOs would take some
> >>> work (if at all desired), but that is not a reason to be adding custom
> >>> implementations that violates the kernel's power policies and new ABIs
> >>> that would need to be maintained forever.
> (...)
> >>> Meanwhile you can (should) use gpio-keys if you need to wake your system
> >>> on gpio events.
> >>
> >> We had that discussion and I don't think GPIO keys is the right solution
> >> for every use-case.
> >
> > Sorry, it has been a while - can you remind us of why?
> 
> There are such cases. Of course keys should be handled by GPIO-keys
> and these will trigger the right wakeup events in such cases.
> 
> This is for more esoteric cases: we cannot have a kernel module for
> everything people want to do with GPIOs, and the use case I accept
> is GPIOs used in automatic control etc, think factory lines or doors.
> We can't have a "door" driver or "punch arm" or "fire alarm" driver
> in the kernel. Those are userspace things.
> 
> Still such embedded systems need to be able to go to idle and
> sleep to conerve power, and then they need to put wakeups on
> these GPIOs.
> 
> So it is a feature userspace needs, though as with much of the
> sysfs ABI it is very often abused for things like keys and LEDs which
> is an abomination but we can't do much about it :(

Thanks for clearing that up.
What does that mean for this patch? Are we going ahead, accepting the
extension of this API or do all these use-cases have to wait for the
rewrite of a proper GPIO userspace interface?

	Thanks,
	Sören
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