linux-kernel - Re: [PATCH v2] gpio: interrupt consistency check for OF GPIO IRQs

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Date:	Fri, 23 Aug 2013 14:55:41 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tomasz Figa <tomasz.figa@...il.com>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	Lars Poeschel <larsi@....tu-dresden.de>,
	Lars Poeschel <poeschel@...onage.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>,
	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 v2] gpio: interrupt consistency check for OF GPIO IRQs

On 08/23/2013 01:55 PM, Tomasz Figa wrote:
> On Friday 23 of August 2013 13:52:20 Stephen Warren wrote:
>> On 08/23/2013 12:45 PM, Linus Walleij wrote:
>>> On Thu, Aug 22, 2013 at 11:10 PM, Stephen Warren 
> <swarren@...dotorg.org> wrote:
>>>> On 08/21/2013 05:36 PM, Linus Walleij wrote:
>>>>> On Thu, Aug 22, 2013 at 1:10 AM, Stephen Warren
>>>>> <swarren@...dotorg.org> wrote: [Me]
>>>>>
>>>>>>>> check if these in turn reference the interrupt-controller, and
>>>>>>>> if they do, loop over the interrupts used by that child and
>>>>>>>> perform gpio_request() and gpio_direction_input() on these,
>>>>>>>> making them unreachable from the GPIO side.
>>>>>>
>>>>>> What about bindings that require a GPIO to be specified, yet don't
>>>>>> allow an IRQ to be specified, and the driver internally does
>>>>>> perform gpio_to_irq() on it? I don't think one can detect that
>>>>>> case.
>>>>>
>>>>> This is still allowed. Consumers that prefer to have a GPIO
>>>>> passed and convert it to IRQ by that call can still do so,
>>>>> they will know what they're doing and will not cause the
>>>>> double-command situation that we're trying to solve.
>>>>
>>>> Why not? There are certainly drivers in the kernel which request a
>>>> GPIO
>>>> as both a GPIO and as an (dual-edge) interrupt, so that they can read
>>>> the GPIO input whenever the IRQ goes off, in order to determine the
>>>> pin
>>>> state. This is safer against high-latency or lost interrupts.
>>>
>>> Yes? Are we talking past each other here?
>>>
>>> This is a perfectly OK thing to do as long as it is done like
>>> this:
>>>
>>> request_gpio(gpio);
>>> gpio_direction_input(gpio);
>>> request_irq(gpio_to_irq(gpio));
>>
>> But I'm not aware that there's a rule saying it's illegal to:
>>
>> request_irq(gpio_to_irq(gpio));
>> request_gpio(gpio);
>> gpio_direction_input(gpio);
> 
> Well, at least on Samsung platforms it is illegal to do so, because 
> gpio_direction_input() would override the interrupt+input function set by 
> setup done in request_irq() with normal input function, thus breaking the 
> interrupt.

Assuming that Linux has no general rule that requires a specific order,
isn't that simply a bug in the Samsung platforms? After all, a
completely generic cross-platform driver, which could touch both GPIO
and IRQ, would be written to any Linux-imposed rules, not any
Samsung-platform-imposed rules.

> We are still to implement some sanity check to disallow (or ignore) this 
> if the pin is already configured as an interrupt.

OK good, so it sounds like this is a temporary issue.
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