linux-kernel - Re: [RFC] gpio/omap: auto-setup a GPIO when used as an IRQ

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Date:	Mon, 23 Sep 2013 18:31:50 +0200
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Santosh Shilimkar <santosh.shilimkar@...com>,
	Kevin Hilman <khilman@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Lars Poeschel <larsi@....tu-dresden.de>,
	Grant Likely <grant.likely@...aro.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>,
	Balaji T K <balajitk@...com>,
	Tony Lindgren <tony@...mide.com>,
	Jon Hunter <jgchunter@...il.com>, linux-gpio@...r.kernel.org,
	linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] gpio/omap: auto-setup a GPIO when used as an IRQ

On 09/23/2013 06:14 PM, Stephen Warren wrote:
> On 09/22/2013 08:40 AM, Javier Martinez Canillas wrote:
>> To use a GPIO pin as an interrupt line, two previous configurations
>> have to be made:
>> 
>> a) Map the GPIO pin as an interrupt line into the Linux irq space
>> b) Enable the GPIO bank and configure the GPIO direction as input
>> 
>> Most GPIO/IRQ chip drivers just create a mapping for every single
>> GPIO pin with irq_create_mapping() on .probe so users usually can
>> assume a) and only have to do b) by using the following sequence:
>> 
>> gpio_request(gpio, "foo IRQ");
>> gpio_direction_input(gpio);
>> 
>> and then request a IRQ with:
>> 
>> irq = gpio_to_irq(gpio);
>> request_irq(irq, ...);
>> 
>> Some drivers know that their IRQ line is being driven by a GPIO
>> and use a similar sequence as the described above but others are
>> not aware or don't care wether their IRQ is a real line from an
>> interrupt controller or a GPIO pin acting as an IRQ.
>> ...
> 
> I think that explanation is a bit like retro-actively implying that
> drivers /should/ be aware of whether their IRQ is a GPIO or not, and
> should be acting differently. However, they should not.
>

I know the patch description is rather verbose but since we have been discussing
this a lot and people have different opinions I wanted to explain some context
and the motivation for the patch.

> I would much rather see a simpler patch description along the lines of:
> 
> The OMAP GPIO controller HW requires that a pin be configured in GPIO
> mode in order to operate as an interrupt input. Since drivers should not
> be aware of whether an interrupt pin is also a GPIO or not, the HW
> should be fully configured/enabled as an IRQ if a driver solely uses IRQ
> APIs such as request_irq, and never calls any GPIO-related APIs. As
> such, add the missing HW setup to the OMAP GPIO controller's irq_chip
> driver.
> 

Thanks for the suggestion, I'll use something like that when I do a proper post
as a PATCH and not RFC.

> The code change looks like it does what I would expect though.
> 

Great, let's see what is the feedback from Santosh and Kevin about the
implementation since they are the maintainers of this driver.

I really hope we can find a solution to this long standing issue.

Thanks a lot and best regards,
Javier
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