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 ::= [gpio-list] single-gpio ::= gpio-phandle : phandle to gpio controller node gpio-specifier : Array of #gpio-cells specifying specific gpio (controller specific) GPIO properties should be named "[-]gpios", with being the purpose of this GPIO for the device. While a non-existent is considered valid for compatibility reasons (resolving to the "gpios" property), it is not allowed for new bindings. Also, GPIO properties named "[-]gpio" are valid and old bindings use it, but are only supported for compatibility reasons and should not be used for newer bindings since it has been deprecated. 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. Most controllers are however specifying a generic flag bitfield in the last cell, so for these, 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. Optional standard bitfield specifiers for the last cell: - Bit 0: 0 means active high, 1 means active low - Bit 1: 1 means single-ended wiring, see: https://en.wikipedia.org/wiki/Single-ended_triode When used with active-low, this means open drain/collector, see: https://en.wikipedia.org/wiki/Open_collector When used with active-high, this means open source/emitter 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 following 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. Some system-on-chips (SoCs) use the concept of GPIO banks. A GPIO bank is an instance of a hardware IP core on a silicon die, usually exposed to the programmer as a coherent range of I/O addresses. Usually each such bank is exposed in the device tree as an individual gpio-controller node, reflecting the fact that the hardware was synthesized by reusing the same IP block a few times over. Optionally, a GPIO controller may have a "ngpios" property. This property indicates the number of in-use slots of available slots for GPIOs. The typical example is something like this: the hardware register is 32 bits wide, but only 18 of the bits have a physical counterpart. The driver is generally written so that all 32 bits can be used, but the IP block is reused in a lot of designs, some using all 32 bits, some using 18 and some using 12. In this case, setting "ngpios = <18>;" informs the driver that only the first 18 GPIOs, at local offset 0 .. 17, are in use. If these GPIOs do not happen to be the first N GPIOs at offset 0...N-1, an additional bitmask is needed to specify which GPIOs are actually in use, and which are dummies. The bindings for this case has not yet been specified, but should be specified if/when such hardware appears. Optionally, a GPIO controller may have a "gpio-line-names" property. This is an array of strings defining the names of the GPIO lines going out of the GPIO controller. This name should be the most meaningful producer name for the system, such as a rail name indicating the usage. Package names such as pin name are discouraged: such lines have opaque names (since they are by definition generic purpose) and such names are usually not very helpful. For example "MMC-CD", "Red LED Vdd" and "ethernet reset" are reasonable line names as they describe what the line is used for. "GPIO0" is not a good name to give to a GPIO line. Placeholders are discouraged: rather use the "" (blank string) if the use of the GPIO line is undefined in your design. The names are assigned starting from line offset 0 from left to right from the passed array. An incomplete array (where the number of passed named are less than ngpios) will still be used up until the last provided valid line index. Example: gpio-controller@00000000 { compatible = "foo"; reg = <0x00000000 0x1000>; gpio-controller; #gpio-cells = <2>; ngpios = <18>; gpio-line-names = "MMC-CD", "MMC-WP", "VDD eth", "RST eth", "LED R", "LED G", "LED B", "Col A", "Col B", "Col C", "Col D", "Row A", "Row B", "Row C", "Row D", "NMI button", "poweroff", "reset"; } The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism providing automatic GPIO request and configuration as part of the gpio-controller's driver probe function. Each GPIO hog definition is represented as a child node of the GPIO controller. Required properties: - gpio-hog: A property specifying that this child node represents a GPIO hog. - gpios: Store the GPIO information (id, flags, ...) for each GPIO to affect. Shall contain an integer multiple of the number of cells specified in its parent node (GPIO controller node). Only one of the following properties scanned in the order shown below. This means that when multiple properties are present they will be searched in the order presented below and the first match is taken as the intended configuration. - input: A property specifying to set the GPIO direction as input. - output-low A property specifying to set the GPIO direction as output with the value low. - output-high A property specifying to set the GPIO direction as output with the value high. Optional properties: - line-name: The GPIO label name. If not present the node name is used. 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>; line_b { gpio-hog; gpios = <6 0>; output-low; line-name = "foo-bar-gpio"; }; }; 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 ::= [gpio-range-list] single-gpio-range ::= | numeric-gpio-range ::= named-gpio-range ::= '<0 0>' pinctrl-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 and set to 0), the property gpio-ranges-group-names contains one string for every single-gpio-range in gpio-ranges: gpiorange-names-list ::= [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".