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Commit ede033e1 authored by Thomas Petazzoni's avatar Thomas Petazzoni Committed by Linus Walleij
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dt-bindings: gpio: document the new pull-up/pull-down flags 



This commit extends the flags that can be used in GPIO specifiers to
indicate if a pull-up resistor or pull-down resistor should be
enabled.

While some pinctrl DT bindings already offer the capability of
configuring pull-up/pull-down resistors at the pin level, a number of
simple GPIO controllers don't have any pinmuxing capability, and
therefore do not rely on the pinctrl DT bindings.

Such simple GPIO controllers however sometimes allow to configure
pull-up and pull-down resistors on a per-pin basis, and whether such
resistors should be enabled or not is a highly board-specific HW
characteristic.

By using two additional bits of the GPIO flag specifier, we can easily
allow the Device Tree to describe which GPIOs should have their
pull-up or pull-down resistors enabled. Even though the two options
are mutually exclusive, we still need two bits to encode at least
three states: no pull-up/pull-down, pull-up, pull-down.

Signed-off-by: default avatarThomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
parent bfeffd15

Documentation/devicetree/bindings/gpio/gpio.txt

+12 −0
Original line number Diff line number Diff line
@@ -67,6 +67,18 @@ Optional standard bitfield specifiers for the last cell: 
           https://en.wikipedia.org/wiki/Open_collector

- Bit 3: 0 means the output should be maintained during sleep/low-power mode

         1 means the output state can be lost during sleep/low-power mode

- Bit 4: 0 means no pull-up resistor should be enabled

         1 means a pull-up resistor should be enabled

         This setting only applies to hardware with a simple on/off

         control for pull-up configuration. If the hardware has more

         elaborate pull-up configuration, it should be represented

         using a pin control binding.

- Bit 5: 0 means no pull-down resistor should be enabled

         1 means a pull-down resistor should be enabled

         This setting only applies to hardware with a simple on/off

         control for pull-down configuration. If the hardware has more

         elaborate pull-down configuration, it should be represented

         using a pin control binding.



1.1) GPIO specifier best practices

----------------------------------

include/dt-bindings/gpio/gpio.h

+6 −0
Original line number Diff line number Diff line
@@ -33,4 +33,10 @@ 
#define GPIO_PERSISTENT 0

#define GPIO_TRANSITORY 8



/* Bit 4 express pull up */

#define GPIO_PULL_UP 16



/* Bit 5 express pull down */

#define GPIO_PULL_DOWN 32



#endif