From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dirk Behme Subject: Re: [PATCH v2] Documentation: gpio: consumer: describe active low property Date: Sat, 15 Aug 2015 07:46:48 +0200 Message-ID: <55CED248.101@gmail.com> References: <1437199327-4410-1-git-send-email-dirk.behme@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-wi0-f180.google.com ([209.85.212.180]:37546 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750806AbbHOFq4 (ORCPT ); Sat, 15 Aug 2015 01:46:56 -0400 Received: by wibhh20 with SMTP id hh20so38656068wib.0 for ; Fri, 14 Aug 2015 22:46:55 -0700 (PDT) In-Reply-To: <1437199327-4410-1-git-send-email-dirk.behme@gmail.com> Sender: linux-gpio-owner@vger.kernel.org List-Id: linux-gpio@vger.kernel.org To: linux-gpio@vger.kernel.org Cc: Alexandre Courbot , Linus Walleij On 18.07.2015 08:02, Dirk Behme wrote: > I've been searching for any documentation of 'the active-low property of a GPIO' > already mentioned in this documenation. But couldn't find any. Add it. > > Sigend-off-by: Dirk Behme > Acked-by: Alexandre Courbot > --- > Changes in v2: Incorporate the review comments from Alexandre. > > Documentation/gpio/consumer.txt | 33 +++++++++++++++++++++++++++++++++ > 1 file changed, 33 insertions(+) > > diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt > index 75542b9..df7c51a 100644 > --- a/Documentation/gpio/consumer.txt > +++ b/Documentation/gpio/consumer.txt > @@ -237,6 +237,39 @@ Note that these functions should only be used with great moderation ; a driver > should not have to care about the physical line level. > > > +The active-low property > +----------------------- > + > +As a driver should not have to care about the physical line level, all of the > +gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with > +the *logical* value. With this they take the active-low property into account. > +This does mean that they check whether the GPIO is configured to be active-low. > +And if so, they manipulate the passed value before the physical line level is > +driven. > + > +With this, all the gpiod_set_(array)_value_xxx() functions interpret the parameter > +"value" as "active" ("1") or "inactive" ("0"). The physical line level will be > +driven accordingly. > + > +As an example, if the active-low poperty for a dedicated GPIO is set, and the > +gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level will be > +driven low. > + > +To summarize: > + > +Function (example) active-low proporty physical line > +gpiod_set_raw_value(desc, 0); don't care low > +gpiod_set_raw_value(desc, 1); don't care high > +gpiod_set_value(desc, 0); default (active-high) low > +gpiod_set_value(desc, 1); default (active-high) high > +gpiod_set_value(desc, 0); active-low high > +gpiod_set_value(desc, 1); active-low low > + > +Please note again that the set_raw/get_raw functions should be avoided as much > +as possible, especially by drivers which should not care about the actual physical > +line level and worry about the logical value instead. > + > + > Set multiple GPIO outputs with a single function call > ----------------------------------------------------- > The following functions set the output values of an array of GPIOs: Any further comments on this? Could this be applied? Dirk