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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 <>
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

+ "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.

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