linux-kernel - Re: [PATCH 1/3] gpiolib: add gpio_set

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Message-ID: <20100301103550.GA24518@rakim.wolfsonmicro.main>
Date:	Mon, 1 Mar 2010 10:35:50 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Ben Gardner <gardner.ben@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andres Salomon <dilinger@...labora.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jani Nikula <ext-jani.1.nikula@...ia.com>
Subject: Re: [PATCH 1/3] gpiolib: add gpio_set_direction()

On Sat, Feb 27, 2010 at 09:51:08AM -0800, David Brownell wrote:
> On Saturday 27 February 2010, Mark Brown wrote:

> > Indeed, but some devices do implement a distinct tristate state for  
> > input mode pins (disabling interrupt generation logic and so on for  
> > example).

> That's a pretty sloppy usage of the term "tristate" ... yeah, there
> are people who take glee in abusing terminology to introduce confusion,
> and some of them write technical manuals with little regard to normal
> usage of terms (or trademarks, which do exist for "tristate").

It's a bit clearer when the pins have multiple functions of which GPIO
is only one - normally the tristate is something that applies over all
the functions of the GPIO.

> IRQ generation logic should be disabled until request_irq() code paths
> report otherwise.   And regardless, whether a GPIO triggers an IRQ has
> nothing at all to do with its "direction".

This is an internal Linux implementation issue rather than a hardware
one - that was just an example one of the things that tristating the pin
rather than just putting it into input mode does.
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