linux-kernel - Re: [PATCH] input: gpio_keys: Don't report events on gpio failure

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Date:	Mon, 17 Aug 2015 12:34:47 -0700
From:	Bjorn Andersson <bjorn.andersson@...ymobile.com>
To:	Alexandre Courbot <gnurou@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH] input: gpio_keys: Don't report events on gpio failure

On Sun 16 Aug 23:59 PDT 2015, Alexandre Courbot wrote:

> On Thu, Aug 13, 2015 at 10:06 PM, Linus Walleij
> <linus.walleij@...aro.org> wrote:
> > On Tue, Aug 11, 2015 at 12:41 AM, Bjorn Andersson
> > <bjorn.andersson@...ymobile.com> wrote:
> >
> >> But then the question first goes to Linus & co.
> >>
> >> gpio_chip->get() can return a negative value to indicate errors (and did
> >> so in this case), all parts of the API seems indicates that we can get
> >> an error (int vs bool).
> >
> > Ooops.
> >
> >> Should we change _gpiod_get_raw_value() to propagate this error?
> >
> > Yes for now. Can you patch it? :)
> >
> >>  Or
> >> should we just ignore this issue and propagate an error as GPIO high
> >> reading?
> >
> > I don't know about the future. In some sense GPIOs are so smallish
> > resources that errorhandling every call to read/write them seem to
> > be a royal PITA. That is why I wanted to switch them to bool and get
> > rid of the problem, but now I also see that maybe that was not such a
> > smart idea, if errors do occur on the set/get_value path.
> 
> Nowadays GPIOs may reside at the other end of an i2c bus, which means
> that even the simplest operation like reading a GPIO value can
> potentially fail. And it will probably not get better - wait until we
> implement GPIO-over-IP! :)
> 

Now that's progress! I can't wait ;)

> So I'd say it makes sense to propagate errors returned by the driver's
> get() hook. This might contradict some of our earlier statements about
> simplifying the GPIO API, but is preferrable to having to make a
> decision as to which valid value to return if the driver fails...
> 

Sounds good.

As we're patching up _gpiod_get_raw_value(), is the lack of a get()
implementation the same as a LOW or is that -ENOTSUPP?

> It should then be made very clear in the documentation that the only
> positive values ever returned by the GPIO API will be 0 and 1 (we
> already have a clamping mechanism for that IIRC), and that negative
> values are propagated as-is.
> 

That makes sense. I'm however not able to find such clamping
macro/mechanism and it would be very beneficial here...

> Linus, does that seem reasonable to you? Does anyone has the intention
> to address that one or should I add it to my short-term TODO list?

If you have some input on above (is lack of get() an error) I can hack
up the patch.

Regards,
Bjorn
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