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

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Date:	Mon, 29 Jul 2013 22:30:23 -0600
From:	Grant Likely <grant.likely@...aro.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Alexander Holler <holler@...oftware.de>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	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>
Subject: Re: [PATCH] RFC: interrupt consistency check for OF GPIO IRQs

On Mon, Jul 29, 2013 at 6:36 AM, Linus Walleij <linus.walleij@...aro.org> wrote:
> To solve this dilemma, perform an interrupt consistency check
> when adding a GPIO chip: if the chip is both gpio-controller and
> interrupt-controller, walk all children of the device tree,
> check if these in turn reference the interrupt-controller, and
> if they do, loop over the interrupts used by that child and
> perform gpio_reques() and gpio_direction_input() on these,
> making them unreachable from the GPIO side.

Ugh, that's pretty awful, and it doesn't actually solve the root
problem of the GPIO and IRQ subsystems not cooperating. It's also a
very DT-centric solution even though we're going to see the exact same
issue on ACPI machines.

We have to solve the problem in a better way than that. Rearranging
your patch description, here are some of the points you brought up so
I can comment on them...

> This has the following undesired effects:
>
> - The GPIOlib subsystem is not aware that the line is in use
>   and willingly lets some other consumer perform gpio_request()
>   on it, leading to a complex resource conflict if it occurs.

If a gpio line is being both requested as a gpio and used as an
interrupt line, then either a) it's a bug, or b) the gpio line needs
to be used as input only so it is compatible with irq usage. b) should
be supportable.

> - The GPIO debugfs file claims this GPIO line is "free".

Surely we can fix this. I still don't see a problem of having the
controller request the gpio when it is claimed as an irq if we can get
around the problem of another user performing a /valid/ request on the
same GPIO line. The solution may be to have a special form of request
or flag that allows it to be shared.

> - The line direction of the interrupt GPIO line is not
>   explicitly set as input, even though it is obvious that such
>   a line need to be set up in this way, often making the system
>   depend on boot-on defaults for this kind of settings.

Should also be solvable if the gpio request problem is solved.

g.
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