linux-kernel - Re: [PATCH v3] gpio: interrupt consistency check for OF GPIO IRQs

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Message-ID: <CACRpkdZ7E7MGppbkTiObvTDHdmphnbysMKVc1OZjsPXKVuKttQ@mail.gmail.com>
Date:	Tue, 24 Sep 2013 10:31:41 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Lars Poeschel <poeschel@...onage.de>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Mark Brown <broonie@...nel.org>,
	Lars Poeschel <larsi@....tu-dresden.de>,
	Grant Likely <grant.likely@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Kumar Gala <galak@...eaurora.org>,
	Pawel Moll <pawel.moll@....com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Enric Balletbo i Serra <eballetbo@...il.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Kevin Hilman <khilman@...aro.org>,
	Balaji T K <balajitk@...com>,
	Tony Lindgren <tony@...mide.com>,
	Jon Hunter <jgchunter@...il.com>, joelf@...com,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
Subject: Re: [PATCH v3] gpio: interrupt consistency check for OF GPIO IRQs

On Mon, Sep 23, 2013 at 10:21 PM, Stephen Warren <swarren@...dotorg.org> wrote:
> On 09/23/2013 02:01 PM, Linus Walleij wrote:

>> And how to you block the same line from being gpio_request()ed
>> and set as output?
>
> To be honest, I really don't think this problem is terribly likely to
> occur, so I'm really not convinced that it's worth putting a lot of
> effort into solving it.

I have a different opionion, I think this is important. As GPIO
subsystem maintainer I need to be convinced of the integrity
of the system.

> If the problem does occur, it's trivial to see that this has happened by
> looking at /proc/interrupts and /sys/kernel/debug/gpio,

I basically want /sys/kernel/debug/gpio to say if a certain line
is tied for IRQ.

> That driver needs to maintain some state that indicates which of its
> IRQs have been requested. Any time a GPIO request (I mean e.g.
> set_output() not request_gpio)) comes in, the request needs to be
> validated against that IRQ usage state. If there's a conflict, deny the
> GPIO request.

I think this should be done by gpiolib, and I think it is trivial
given the right APIs. Putting it in the drivers will just create
an array of similar-look Rube Goldberg-machines and code
duplication. There is no point.

> Now, it's quite possible that the code to maintain this state and
> perform the checks will be similar/common across multiple drivers. If
> so, by all means implement the code somewhere common, and have the
> various irq_chip/gpio_chip drivers call into it.

And this is what we should do in gpiolib.

> The main thing is that all of this has to be driven/controlled/enabled
> by the gpio_chip/irq_chip driver itself, not as some global/blanket
> feature of the GPIO or IRQ subsystems.

Sure.

> Perhaps rather than having the gpio_chip/irq_chip drivers physically
> implement a function which calls this common code, they could set some
> flags/data/... in the struct gpio_chip/irq_chip indicating that they
> desire the core code that implements the error-checking to be enabled.

I think it should more be like a function they can call to flag
a GPIO as used for IRQ.

Yours,
Linus Walleij
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