linux-kernel - Re: gpio patches in mmotm

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Message-ID: <Pine.LNX.4.64.0803181717240.5022@axis700.grange>
Date:	Tue, 18 Mar 2008 17:31:16 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@...gutronix.de>
To:	Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>
cc:	David Brownell <david-b@...bell.net>, linux-kernel@...r.kernel.org
Subject: Re: gpio patches in mmotm

Please, do not trim the CC: list. I've also added lkml.

On Tue, 18 Mar 2008, Uwe Kleine-KЖnig wrote:

> Guennadi Liakhovetski wrote:
> > On Mon, 17 Mar 2008, Uwe Kleine-KЖnig wrote:
> > 
> > > I'm nure sure if I like gpio_is_valid().  When do you think it should be
> > > used?  (i.e. in which situations gpio_request doesn't do the right
> > > thing?)
> > 
> > For example, in situations similar to what I have in mt9m001 and mt9v022 
> > camera drivers. Those cameras can be built with an i2c gpio extender, 
> > which can be used to switch between 8 and 10 bit data bus widths. But that 
> > extender is not always available. So, those drivers request a gpio, and if 
> > it is not available on the system, the gpio_is_valid() test fails.
> I found your patch, but no tree where it applies.  Can you point me to a
> tree where it applies?

These drivers are currently in the v4l-dvb tree 
http://git.kernel.org/?p=linux/kernel/git/mchehab/v4l-dvb.git;a=summary in 
the devel branch.

> Why isn't it enough that gpio_request fails in such a situation?

I'm storing the GPIO number locally, and if the system doesn't have a 
valid GPIO for me, I'm storing an invalid GPIO number. Then at any time if 
the GPIO has to be used, I just verify if gpio_is_valid(), and if not, 
return an error code for this request, but the driver remains otherwise 
functional.

Thanks
Guennadi
---
Guennadi Liakhovetski
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