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

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Message-ID: <524068D4.5040909@wwwdotorg.org>
Date:	Mon, 23 Sep 2013 10:14:12 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
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 09/22/2013 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 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.

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