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    Subject[PATCH V1 2/3] Documentation: gpio: Add details of open-drain configuration
    Date
    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@nvidia.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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