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

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Date:	Tue, 13 Aug 2013 08:22:58 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	Lars Poeschel <larsi@....tu-dresden.de>
Cc:	poeschel@...onage.de, grant.likely@...aro.org,
	linus.walleij@...aro.org, linux-gpio@...r.kernel.org,
	linux-kernel@...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>,
	Balaji T K <balajitk@...com>,
	Tony Lindgren <tony@...mide.com>,
	Jon Hunter <jgchunter@...il.com>
Subject: Re: [PATCH v2] RFC: interrupt consistency check for OF GPIO IRQs

Lars Poeschel <larsi@....tu-dresden.de> writes:

> From: Linus Walleij <linus.walleij@...aro.org>
>
> Currently the kernel is ambigously treating GPIOs and interrupts
> from a GPIO controller: GPIOs and interrupts are treated as
> orthogonal. This unfortunately makes it unclear how to actually
> retrieve and request a GPIO line or interrupt from a GPIO
> controller in the device tree probe path.
>
> In the non-DT probe path it is clear that the GPIO number has to
> be passed to the consuming device, and if it is to be used as
> an interrupt, the consumer shall performa a gpio_to_irq() mapping
> and request the resulting IRQ number.
>
> In the DT boot path consumers may have been given one or more
> interrupts from the interrupt-controller side of the GPIO chip
> in an abstract way, such that the driver is not aware of the
> fact that a GPIO chip is backing this interrupt, and the GPIO
> side of the same line is never requested with gpio_request().
> A typical case for this is ethernet chips which just take some
> interrupt line which may be a "hard" interrupt line (such as an
> external interrupt line from an SoC) or a cascaded interrupt
> connected to a GPIO line.
>
> 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.

And another reason, which happens on OMAP (not that the others aren't
already enough to make the case):

 - Platform-specific power management code may gate clocks or power to
   unused GPIO banks resulting in faults when accessing a GPIO that
   has not been properly requested via gpio_request().

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

Kevin
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