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: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxx>
---
Documentation/devicetree/bindings/gpio/gpio.txt | 12 ++++++++++++
include/dt-bindings/gpio/gpio.h | 6 ++++++
2 files changed, 18 insertions(+)
diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
index f0ba154b5723..a8895d339bfe 100644
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt
@@ -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
----------------------------------
diff --git a/include/dt-bindings/gpio/gpio.h b/include/dt-bindings/gpio/gpio.h
index 2cc10ae4bbb7..c029467e828b 100644
--- a/include/dt-bindings/gpio/gpio.h
+++ b/include/dt-bindings/gpio/gpio.h
@@ -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
--
2.20.1
