From: Dirk Behme <dirk.behme@gmail.com>
To: linux-gpio@vger.kernel.org
Cc: Dirk Behme <dirk.behme@gmail.com>
Subject: [PATCH] Documentation: gpio: consumer: describe active low property
Date: Sat, 4 Jul 2015 18:19:08 +0200 [thread overview]
Message-ID: <1436026748-4452-1-git-send-email-dirk.behme@gmail.com> (raw)
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 <dirk.behme@gmail.com>
---
Documentation/gpio/consumer.txt | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 75542b9..f1a6e20 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -236,6 +236,32 @@ The active-low state of a GPIO can also be queried using the following call:
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_xxx_value_xxx() functions do 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_xxx_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_xxx_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); n/a low
+gpiod_set_value(desc, 1); n/a high
+gpiod_set_value(desc, 0); active-low high
+gpiod_set_value(desc, 1); active-low low
+
Set multiple GPIO outputs with a single function call
-----------------------------------------------------
--
2.4.5
next reply other threads:[~2015-07-05 8:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-04 16:19 Dirk Behme [this message]
2015-07-14 5:06 ` [PATCH] Documentation: gpio: consumer: describe active low property Alexandre Courbot
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