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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/