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Documentation: gpio: Add details of open-drain/source configuration

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Adding details of open drain(open collector) and open source
(open emitter) 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@nvidia.com>
Reviwed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
This commit is contained in:
Laxman Dewangan 2012-02-17 20:26:20 +05:30 committed by Grant Likely
parent 6e2cf65140
commit 3d2ddfdcf0
1 changed files with 15 additions and 2 deletions
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17
Documentation/gpio.txt
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@ -302,6 +302,8 @@ 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_OPEN_DRAIN - gpio pin is open drain type.
* GPIOF_OPEN_SOURCE - gpio pin is open source type.
since GPIOF_INIT_* are only valid when configured as output, so group valid
combinations as:
@ -310,8 +312,19 @@ 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.
When setting the flag as GPIOF_OPEN_DRAIN then it will assume that pins is
open drain type. Such pins will not be driven to 1 in output mode. It is
require to connect pull-up on such pins. By enabling this flag, gpio lib will
make the direction to input when it is asked to set value of 1 in output mode
to make the pin HIGH. The pin is make to LOW by driving value 0 in output mode.
When setting the flag as GPIOF_OPEN_SOURCE then it will assume that pins is
open source type. Such pins will not be driven to 0 in output mode. It is
require to connect pull-down on such pin. By enabling this flag, gpio lib will
make the direction to input when it is asked to set value of 0 in output mode
to make the pin LOW. The pin is make to HIGH by driving value 1 in output mode.
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: