From ede033e1e863c36729de25b57145fff287415830 Mon Sep 17 00:00:00 2001 From: Thomas Petazzoni Date: Thu, 7 Feb 2019 17:28:55 +0100 Subject: [PATCH] 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: Thomas Petazzoni Signed-off-by: Linus Walleij --- 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 -- 2.30.2