From: Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>
Cc: Jean-Christophe PLAGNIOL-VILLARD
<plagnioj-sclMFOaUSTBWk0Htik3J/w@public.gmane.org>,
Denis Carikli <denis-fO0SIAKYzcbQT0dZR+AlfA@public.gmane.org>,
Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Ian Campbell
<ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>,
Eric B??nard <eric-fO0SIAKYzcbQT0dZR+AlfA@public.gmane.org>,
Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>,
Jingoo Han <jg1.han-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
Rob Herring <rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org>,
Richard Purdie <rpurdie-Fm38FmjxZ/leoWH0uzbU5w@public.gmane.org>,
Laurent Pinchart
<laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>,
Sascha Hauer <kernel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>,
linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
Lothar Wa??mann
<LW-bxm8fMRDkQLDiMYJYoSAnRvVK+yQ3ZXh@public.gmane.org>
Subject: Re: [PATCHv4] video: backlight: gpio-backlight: Add DT support.
Date: Wed, 23 Oct 2013 22:08:09 +0200 [thread overview]
Message-ID: <20131023200808.GC8828@mithrandir> (raw)
In-Reply-To: <5267FE02.6000001-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>
[-- Attachment #1: Type: text/plain, Size: 1020 bytes --]
On Wed, Oct 23, 2013 at 05:49:06PM +0100, Stephen Warren wrote:
> On 10/23/2013 02:42 PM, Jean-Christophe PLAGNIOL-VILLARD wrote:
> ...
> > For me gpio_get_value can return the value of a an output gpio but this need
> > to be checked with LinusW
>
> That's certainly not true for all possible GPIO controllers; there are
> at least some that can't read either:
>
> * The value of the physical wire, if the GPIO is configured as an output.
>
> * The value that the GPIO controller is driving as an output.
My point originally was that since it's an output pin, you need to
configure it as an output before you can use it. The way to do that in
Linux is to call gpio_direction_output(). But that will automatically
also force the output value to whatever you specify as the second
parameter.
I suppose that could be remedied by adding a separate function that
doesn't set the value, but as Stephen points out, reading the value of
an output pin may not be supported on all hardware.
Thierry
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WARNING: multiple messages have this Message-ID (diff)
From: thierry.reding@gmail.com (Thierry Reding)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCHv4] video: backlight: gpio-backlight: Add DT support.
Date: Wed, 23 Oct 2013 22:08:09 +0200 [thread overview]
Message-ID: <20131023200808.GC8828@mithrandir> (raw)
In-Reply-To: <5267FE02.6000001@wwwdotorg.org>
On Wed, Oct 23, 2013 at 05:49:06PM +0100, Stephen Warren wrote:
> On 10/23/2013 02:42 PM, Jean-Christophe PLAGNIOL-VILLARD wrote:
> ...
> > For me gpio_get_value can return the value of a an output gpio but this need
> > to be checked with LinusW
>
> That's certainly not true for all possible GPIO controllers; there are
> at least some that can't read either:
>
> * The value of the physical wire, if the GPIO is configured as an output.
>
> * The value that the GPIO controller is driving as an output.
My point originally was that since it's an output pin, you need to
configure it as an output before you can use it. The way to do that in
Linux is to call gpio_direction_output(). But that will automatically
also force the output value to whatever you specify as the second
parameter.
I suppose that could be remedied by adding a separate function that
doesn't set the value, but as Stephen points out, reading the value of
an output pin may not be supported on all hardware.
Thierry
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next prev parent reply other threads:[~2013-10-23 20:08 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-18 15:04 [PATCH 01/11] of: add vendor prefix for Eukréa Electromatique Denis Carikli
2013-10-18 15:04 ` Denis Carikli
2013-10-18 15:04 ` [PATCH 02/11] video: imxfb: Introduce regulator support Denis Carikli
2013-10-18 15:04 ` Denis Carikli
2013-10-19 10:45 ` Jean-Christophe PLAGNIOL-VILLARD
2013-10-19 10:45 ` Jean-Christophe PLAGNIOL-VILLARD
[not found] ` <20131019104555.GI18477-HVbc7XotTAhnXn40ka+A6Q@public.gmane.org>
2013-10-21 9:13 ` [PATCHv4] video: backlight: gpio-backlight: Add DT support Denis Carikli
2013-10-21 9:13 ` Denis Carikli
[not found] ` <1382346813-8449-1-git-send-email-denis-fO0SIAKYzcbQT0dZR+AlfA@public.gmane.org>
2013-10-21 22:48 ` Laurent Pinchart
2013-10-21 22:48 ` Laurent Pinchart
2013-10-22 5:11 ` Jean-Christophe PLAGNIOL-VILLARD
2013-10-22 5:11 ` Jean-Christophe PLAGNIOL-VILLARD
2013-10-22 4:58 ` Jean-Christophe PLAGNIOL-VILLARD
2013-10-22 4:58 ` Jean-Christophe PLAGNIOL-VILLARD
[not found] ` <20131022045833.GB17512-HVbc7XotTAhnXn40ka+A6Q@public.gmane.org>
2013-10-22 7:23 ` Thierry Reding
2013-10-22 7:23 ` Thierry Reding
2013-10-22 15:34 ` Jean-Christophe PLAGNIOL-VILLARD
2013-10-22 15:34 ` Jean-Christophe PLAGNIOL-VILLARD
[not found] ` <20131022153445.GD17512-HVbc7XotTAhnXn40ka+A6Q@public.gmane.org>
2013-10-22 20:01 ` Thierry Reding
2013-10-22 20:01 ` Thierry Reding
2013-10-23 13:42 ` Jean-Christophe PLAGNIOL-VILLARD
2013-10-23 13:42 ` Jean-Christophe PLAGNIOL-VILLARD
[not found] ` <20131023134236.GE17512-HVbc7XotTAhnXn40ka+A6Q@public.gmane.org>
2013-10-23 16:49 ` Stephen Warren
2013-10-23 16:49 ` Stephen Warren
[not found] ` <5267FE02.6000001-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>
2013-10-23 20:08 ` Thierry Reding [this message]
2013-10-23 20:08 ` Thierry Reding
2013-10-23 16:51 ` Stephen Warren
2013-10-23 16:51 ` Stephen Warren
[not found] ` <5267FE81.3070201-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>
2013-10-23 20:20 ` Thierry Reding
2013-10-23 20:20 ` Thierry Reding
2013-10-23 22:38 ` Laurent Pinchart
2013-10-23 22:38 ` Laurent Pinchart
2013-10-24 11:05 ` Thierry Reding
2013-10-24 11:05 ` Thierry Reding
[not found] ` <20131024110524.GB11296-AwZRO8vwLAwmlAP/+Wk3EA@public.gmane.org>
2013-10-25 13:57 ` Laurent Pinchart
2013-10-25 13:57 ` Laurent Pinchart
2013-10-31 23:44 ` Jingoo Han
2013-10-31 23:44 ` Jingoo Han
[not found] ` <003701ced693$2f856150$8e9023f0$%han-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
2013-11-01 9:57 ` Thierry Reding
2013-11-01 9:57 ` Thierry Reding
[not found] ` <20131101095754.GJ27864-AwZRO8vwLAwmlAP/+Wk3EA@public.gmane.org>
2013-11-04 0:20 ` Jingoo Han
2013-11-04 0:20 ` Jingoo Han
2013-10-31 23:37 ` Jingoo Han
2013-10-31 23:37 ` Jingoo Han
[not found] ` <001e01ced692$267a6d90$736f48b0$%han-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
2013-11-01 10:13 ` Thierry Reding
2013-11-01 10:13 ` Thierry Reding
[not found] ` <20131101101346.GK27864-AwZRO8vwLAwmlAP/+Wk3EA@public.gmane.org>
2013-11-06 0:08 ` Laurent Pinchart
2013-11-06 0:08 ` Laurent Pinchart
2013-10-25 20:10 ` Grant Likely
2013-10-25 20:10 ` Grant Likely
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