linux-kernel - Re: [PATCH 2/2] gpio/mxc: implement reading output gpio value

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Message-ID: <CAOMZO5DPYL43QNwYRiGJ_rd2eqm64wg+zACK6viWbC_aFH=qsQ@mail.gmail.com>
Date:	Wed, 5 Aug 2015 15:11:40 -0300
From:	Fabio Estevam <festevam@...il.com>
To:	Eduardo Valentin <edubezval@...il.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Ulises Brindis <ubrindis56@...il.com>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH 2/2] gpio/mxc: implement reading output gpio value

Hi Eduardo,

On Wed, Aug 5, 2015 at 3:02 PM, Eduardo Valentin <edubezval@...il.com> wrote:
>
> Hello Fabio,
>
> On Wed, Aug 05, 2015 at 02:43:05PM -0300, Fabio Estevam wrote:
>> Hi Eduardo,
>>
>> On Wed, Aug 5, 2015 at 2:23 PM, Eduardo Valentin <edubezval@...il.com> wrote:
>> > In current implementation, reading the value of an output gpio
>> > always return 0. The reason is because when a gpio is configured
>>
>> Have you tried setting the SION bit for the pad?
>
> No, I haven't. From the bit description, it looks like it does a
> different thing of what we would achieve with this patch. The SION bit
> is a overwrite to the pad configuration. That is, the pin will be INPUT
> always.
>
> We don't want to force it to be input. We simply want to be able to read
> the value of an output GPIO. That is achievable by reading a different
> register. In case the GPIO is configured as output, the GPIO block
> documentation states its value can be read from GPIO_PSR.
> This approach works fine, as the GPIO will be output and we can still
> read its value.

Setting the SION bit allows you to do exactly that. Please see:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-July/271774.html

Regards,

Fabio Estevam
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