linux-kernel - [PATCH V1 2/3] Documentation: gpio: Add details of open-drain configuration

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Message-Id: <1329114588-15430-3-git-send-email-ldewangan@nvidia.com>
Date:	Mon, 13 Feb 2012 11:59:47 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	grant.likely@...retlab.ca, linus.walleij@...ricsson.com,
	dunlap@...otime.net, lrg@...com,
	broonie@...nsource.wolfsonmicro.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	linux-tegra@...r.kernel.org, ldewangan@...dia.com
Subject: [PATCH V1 2/3] Documentation: gpio: Add details of open-drain configuration

Adding details of open drain configuration of the gpio so that
client can set the pin as open drain at the time of gpio request.

Signed-off-by: Laxman Dewangan <ldewangan@...dia.com>
---
 Documentation/gpio.txt |   21 +++++++++++++++++++--
 1 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index 792faa3..b08933c 100644
--- a/Documentation/gpio.txt
+++ b/Documentation/gpio.txt
@@ -302,6 +302,7 @@ where 'flags' is currently defined to specify the following properties:
 
 	* GPIOF_INIT_LOW	- as output, set initial level to LOW
 	* GPIOF_INIT_HIGH	- as output, set initial level to HIGH
+	* GPIOF_OD		- gpio pin is open drain type.
 
 since GPIOF_INIT_* are only valid when configured as output, so group valid
 combinations as:
@@ -310,8 +311,7 @@ combinations as:
 	* GPIOF_OUT_INIT_LOW	- configured as output, initial level LOW
 	* GPIOF_OUT_INIT_HIGH	- configured as output, initial level HIGH
 
-In the future, these flags can be extended to support more properties such
-as open-drain status.
+In the future, these flags can be extended to support more properties.
 
 Further more, to ease the claim/release of multiple GPIOs, 'struct gpio' is
 introduced to encapsulate all three fields as:
@@ -641,6 +641,13 @@ and have the following read/write attributes:
 		for "rising" and "falling" edges will follow this
 		setting.
 
+	"open_drain" ... reads as either 0 (false) or 1 (true).  Write
+		any nonzero value to make the pin in open drain.
+		By setting open drain to true, the output can be set
+		to HIGH by external PULL UP and setting direction to input.
+		The output will be set to LOW by setting direction to
+		output with value is 0.
+
 GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (for the
 controller implementing GPIOs starting at #42) and have the following
 read-only attributes:
@@ -679,6 +686,9 @@ requested using gpio_request():
 	/* change the polarity of a GPIO node in sysfs */
 	int gpio_sysfs_set_active_low(unsigned gpio, int value);
 
+	/* change the pin to open drain in sysfs */
+	int gpio_sysfs_set_open_drain(unsigned gpio, int value);
+
 After a kernel driver requests a GPIO, it may only be made available in
 the sysfs interface by gpio_export().  The driver can control whether the
 signal direction may change.  This helps drivers prevent userspace code
@@ -698,3 +708,10 @@ differences between boards from user space.  This only affects the
 sysfs interface.  Polarity change can be done both before and after
 gpio_export(), and previously enabled poll(2) support for either
 rising or falling edge will be reconfigured to follow this setting.
+
+Drivers can use gpio_sysfs_set_open_drain() to enable/disable the open
+drain property of that pins. This only affect the sysfs interface.
+The flag will be set as open drain if thsi function is called with value
+of 1. It is recommended to set the open drain property before setting
+the value in output mode so that pin state cn be set properly based
+on the value.
-- 
1.7.1.1

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