linux-kernel - Re: PIXIS gpio controller and gpio flags

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Message-ID: <20080723145650.GA13792@polina.dev.rtsoft.ru>
Date:	Wed, 23 Jul 2008 18:56:50 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Trent Piepho <tpiepho@...escale.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org
Subject: Re: PIXIS gpio controller and gpio flags

On Mon, Jul 21, 2008 at 02:12:20PM -0700, Trent Piepho wrote:
> On Mon, 21 Jul 2008, Anton Vorontsov wrote:
> > On Sat, Jul 19, 2008 at 02:08:01PM -0700, Trent Piepho wrote:
> >> It doesn't look like you have any way to unset the active low flag.  What if
> >> I unload the leds-gpio driver (or another gpio user) and then try to use the
> >> gpio with something else?  The active low flag is stuck on!
> >
> > Why would you want to unset the flags? It is specified in the device
> > tree, and can't be changed. Specifying different flags for the same GPIO
> > would be an error (plus, Linux forbids shared gpios, so you simply can't
> > specify one gpio for several devices).
> 
> You can't use the same gpio for two different things at the same time, but you
> can load a driver, unload it, and then load another.

Hm.. yeah, this might happen. Now I tend to think that transparent
active-low handling wasn't that good idea after all. So, something like
of_gpio_is_active_low(device_node, gpioidx) should be implemented
instead. This function will parse the gpio's = <> flags. Please speak up
if you have any better ideas though.


Thanks for bringing this up,

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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