| Specifying GPIO information for devices |
| ============================================ |
| |
| 1) gpios property |
| ----------------- |
| |
| Nodes that makes use of GPIOs should specify them using one or more |
| properties, each containing a 'gpio-list': |
| |
| gpio-list ::= <single-gpio> [gpio-list] |
| single-gpio ::= <gpio-phandle> <gpio-specifier> |
| gpio-phandle : phandle to gpio controller node |
| gpio-specifier : Array of #gpio-cells specifying specific gpio |
| (controller specific) |
| |
| GPIO properties should be named "[<name>-]gpios", with <name> being the purpose |
| of this GPIO for the device. While a non-existent <name> is considered valid |
| for compatibility reasons (resolving to the "gpios" property), it is not allowed |
| for new bindings. |
| |
| GPIO properties can contain one or more GPIO phandles, but only in exceptional |
| cases should they contain more than one. If your device uses several GPIOs with |
| distinct functions, reference each of them under its own property, giving it a |
| meaningful name. The only case where an array of GPIOs is accepted is when |
| several GPIOs serve the same function (e.g. a parallel data line). |
| |
| The exact purpose of each gpios property must be documented in the device tree |
| binding of the device. |
| |
| The following example could be used to describe GPIO pins used as device enable |
| and bit-banged data signals: |
| |
| gpio1: gpio1 { |
| gpio-controller |
| #gpio-cells = <2>; |
| }; |
| gpio2: gpio2 { |
| gpio-controller |
| #gpio-cells = <1>; |
| }; |
| [...] |
| |
| enable-gpios = <&gpio2 2>; |
| data-gpios = <&gpio1 12 0>, |
| <&gpio1 13 0>, |
| <&gpio1 14 0>, |
| <&gpio1 15 0>; |
| |
| Note that gpio-specifier length is controller dependent. In the |
| above example, &gpio1 uses 2 cells to specify a gpio, while &gpio2 |
| only uses one. |
| |
| gpio-specifier may encode: bank, pin position inside the bank, |
| whether pin is open-drain and whether pin is logically inverted. |
| Exact meaning of each specifier cell is controller specific, and must |
| be documented in the device tree binding for the device. Use the macros |
| defined in include/dt-bindings/gpio/gpio.h whenever possible: |
| |
| Example of a node using GPIOs: |
| |
| node { |
| enable-gpios = <&qe_pio_e 18 GPIO_ACTIVE_HIGH>; |
| }; |
| |
| GPIO_ACTIVE_HIGH is 0, so in this example gpio-specifier is "18 0" and encodes |
| GPIO pin number, and GPIO flags as accepted by the "qe_pio_e" gpio-controller. |
| |
| 1.1) GPIO specifier best practices |
| ---------------------------------- |
| |
| A gpio-specifier should contain a flag indicating the GPIO polarity; active- |
| high or active-low. If it does, the follow best practices should be followed: |
| |
| The gpio-specifier's polarity flag should represent the physical level at the |
| GPIO controller that achieves (or represents, for inputs) a logically asserted |
| value at the device. The exact definition of logically asserted should be |
| defined by the binding for the device. If the board inverts the signal between |
| the GPIO controller and the device, then the gpio-specifier will represent the |
| opposite physical level than the signal at the device's pin. |
| |
| When the device's signal polarity is configurable, the binding for the |
| device must either: |
| |
| a) Define a single static polarity for the signal, with the expectation that |
| any software using that binding would statically program the device to use |
| that signal polarity. |
| |
| The static choice of polarity may be either: |
| |
| a1) (Preferred) Dictated by a binding-specific DT property. |
| |
| or: |
| |
| a2) Defined statically by the DT binding itself. |
| |
| In particular, the polarity cannot be derived from the gpio-specifier, since |
| that would prevent the DT from separately representing the two orthogonal |
| concepts of configurable signal polarity in the device, and possible board- |
| level signal inversion. |
| |
| or: |
| |
| b) Pick a single option for device signal polarity, and document this choice |
| in the binding. The gpio-specifier should represent the polarity of the signal |
| (at the GPIO controller) assuming that the device is configured for this |
| particular signal polarity choice. If software chooses to program the device |
| to generate or receive a signal of the opposite polarity, software will be |
| responsible for correctly interpreting (inverting) the GPIO signal at the GPIO |
| controller. |
| |
| 2) gpio-controller nodes |
| ------------------------ |
| |
| Every GPIO controller node must contain both an empty "gpio-controller" |
| property, and a #gpio-cells integer property, which indicates the number of |
| cells in a gpio-specifier. |
| |
| Example of two SOC GPIO banks defined as gpio-controller nodes: |
| |
| qe_pio_a: gpio-controller@1400 { |
| compatible = "fsl,qe-pario-bank-a", "fsl,qe-pario-bank"; |
| reg = <0x1400 0x18>; |
| gpio-controller; |
| #gpio-cells = <2>; |
| }; |
| |
| qe_pio_e: gpio-controller@1460 { |
| compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank"; |
| reg = <0x1460 0x18>; |
| gpio-controller; |
| #gpio-cells = <2>; |
| }; |
| |
| 2.1) gpio- and pin-controller interaction |
| ----------------------------------------- |
| |
| Some or all of the GPIOs provided by a GPIO controller may be routed to pins |
| on the package via a pin controller. This allows muxing those pins between |
| GPIO and other functions. |
| |
| It is useful to represent which GPIOs correspond to which pins on which pin |
| controllers. The gpio-ranges property described below represents this, and |
| contains information structures as follows: |
| |
| gpio-range-list ::= <single-gpio-range> [gpio-range-list] |
| single-gpio-range ::= <numeric-gpio-range> | <named-gpio-range> |
| numeric-gpio-range ::= |
| <pinctrl-phandle> <gpio-base> <pinctrl-base> <count> |
| named-gpio-range ::= <pinctrl-phandle> <gpio-base> '<0 0>' |
| gpio-phandle : phandle to pin controller node. |
| gpio-base : Base GPIO ID in the GPIO controller |
| pinctrl-base : Base pinctrl pin ID in the pin controller |
| count : The number of GPIOs/pins in this range |
| |
| The "pin controller node" mentioned above must conform to the bindings |
| described in ../pinctrl/pinctrl-bindings.txt. |
| |
| In case named gpio ranges are used (ranges with both <pinctrl-base> and |
| <count> set to 0), the property gpio-ranges-group-names contains one string |
| for every single-gpio-range in gpio-ranges: |
| gpiorange-names-list ::= <gpiorange-name> [gpiorange-names-list] |
| gpiorange-name : Name of the pingroup associated to the GPIO range in |
| the respective pin controller. |
| |
| Elements of gpiorange-names-list corresponding to numeric ranges contain |
| the empty string. Elements of gpiorange-names-list corresponding to named |
| ranges contain the name of a pin group defined in the respective pin |
| controller. The number of pins/GPIOs in the range is the number of pins in |
| that pin group. |
| |
| Previous versions of this binding required all pin controller nodes that |
| were referenced by any gpio-ranges property to contain a property named |
| #gpio-range-cells with value <3>. This requirement is now deprecated. |
| However, that property may still exist in older device trees for |
| compatibility reasons, and would still be required even in new device |
| trees that need to be compatible with older software. |
| |
| Example 1: |
| |
| qe_pio_e: gpio-controller@1460 { |
| #gpio-cells = <2>; |
| compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank"; |
| reg = <0x1460 0x18>; |
| gpio-controller; |
| gpio-ranges = <&pinctrl1 0 20 10>, <&pinctrl2 10 50 20>; |
| }; |
| |
| Here, a single GPIO controller has GPIOs 0..9 routed to pin controller |
| pinctrl1's pins 20..29, and GPIOs 10..19 routed to pin controller pinctrl2's |
| pins 50..59. |
| |
| Example 2: |
| |
| gpio_pio_i: gpio-controller@14B0 { |
| #gpio-cells = <2>; |
| compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank"; |
| reg = <0x1480 0x18>; |
| gpio-controller; |
| gpio-ranges = <&pinctrl1 0 20 10>, |
| <&pinctrl2 10 0 0>, |
| <&pinctrl1 15 0 10>, |
| <&pinctrl2 25 0 0>; |
| gpio-ranges-group-names = "", |
| "foo", |
| "", |
| "bar"; |
| }; |
| |
| Here, three GPIO ranges are defined wrt. two pin controllers. pinctrl1 GPIO |
| ranges are defined using pin numbers whereas the GPIO ranges wrt. pinctrl2 |
| are named "foo" and "bar". |