linux-kernel - Re: [RFC] generic GPIO parameter API

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Message-ID: <Pine.LNX.4.64.0806091906420.25460@axis700.grange>
Date:	Mon, 9 Jun 2008 19:09:00 +0200 (CEST)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
cc:	David Brownell <david-b@...bell.net>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] generic GPIO parameter API

On Mon, 9 Jun 2008, Mark Brown wrote:

> On Mon, Jun 09, 2008 at 06:23:50PM +0200, Guennadi Liakhovetski wrote:
> > On Thu, 5 Jun 2008, David Brownell wrote:
> > > On Monday 02 June 2008, Guennadi Liakhovetski wrote:
> 
> > > > as far as I understand, the current GPIO API only presents very basic GPIO 
> > > > functionality: direction and level reading and writing. Whereas many GPIO 
> > > > controllers have many further configurable parameters: pull-ups and 
> > > > pull-downs, drive strength, slew rate, etc.
> 
> > > Not at all how I'd describe it.  Those omitted mechanisms are part
> > > of pin configuration, in the same way as function multiplexing is.
> > > (That is, assigning a given pin for use as a GPIO, vs hooking it up
> > > to an I2C, MMC, SPI, LCD, I2S, or memory controller.)
> 
> > Yes, on the one hand you're right, this belongs to pin-configuration. But, 
> > otoh, will anyone ever want to change these parameters on non-generic 
> > pins? And should this be allowed? Whereas for GPIOs it clearly makes a 
> 
> They do get configured like that - for example, most I2S devices are
> able to operate as both clock masters and clock slaves.  Often this
> accomplished (at least in part) by configuring the relevant pins as
> inputs or outputs.

The primary purpose of the GPIO-parameter proposal was to allow to 
configure these parameters from the user-space over sysfs by extending the 
gpio-sysfs patch. And I2S master / slave operation should not be 
switchable over sysfs, should it?

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
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