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@@ -4,19 +4,12 @@ Specifying GPIO information for devices
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1) gpios property
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-----------------
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-Nodes that makes use of GPIOs should specify them using one or more
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-properties, each containing a 'gpio-list':
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-
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- gpio-list ::= <single-gpio> [gpio-list]
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- single-gpio ::= <gpio-phandle> <gpio-specifier>
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- gpio-phandle : phandle to gpio controller node
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- gpio-specifier : Array of #gpio-cells specifying specific gpio
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- (controller specific)
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-
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GPIO properties should be named "[<name>-]gpios", with <name> being the purpose
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of this GPIO for the device. While a non-existent <name> is considered valid
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for compatibility reasons (resolving to the "gpios" property), it is not allowed
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-for new bindings.
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+for new bindings. Also, GPIO properties named "[<name>-]gpio" are valid and old
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+bindings use it, but are only supported for compatibility reasons and should not
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+be used for newer bindings since it has been deprecated.
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GPIO properties can contain one or more GPIO phandles, but only in exceptional
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cases should they contain more than one. If your device uses several GPIOs with
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@@ -31,30 +24,28 @@ The following example could be used to describe GPIO pins used as device enable
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and bit-banged data signals:
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gpio1: gpio1 {
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- gpio-controller
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- #gpio-cells = <2>;
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- };
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- gpio2: gpio2 {
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- gpio-controller
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- #gpio-cells = <1>;
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+ gpio-controller;
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+ #gpio-cells = <2>;
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};
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[...]
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- enable-gpios = <&gpio2 2>;
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data-gpios = <&gpio1 12 0>,
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<&gpio1 13 0>,
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<&gpio1 14 0>,
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<&gpio1 15 0>;
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-Note that gpio-specifier length is controller dependent. In the
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-above example, &gpio1 uses 2 cells to specify a gpio, while &gpio2
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-only uses one.
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+In the above example, &gpio1 uses 2 cells to specify a gpio. The first cell is
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+a local offset to the GPIO line and the second cell represent consumer flags,
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+such as if the consumer desire the line to be active low (inverted) or open
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+drain. This is the recommended practice.
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-gpio-specifier may encode: bank, pin position inside the bank,
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-whether pin is open-drain and whether pin is logically inverted.
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-Exact meaning of each specifier cell is controller specific, and must
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-be documented in the device tree binding for the device. Use the macros
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-defined in include/dt-bindings/gpio/gpio.h whenever possible:
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+The exact meaning of each specifier cell is controller specific, and must be
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+documented in the device tree binding for the device, but it is strongly
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+recommended to use the two-cell approach.
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+
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+Most controllers are specifying a generic flag bitfield in the last cell, so
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+for these, use the macros defined in
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+include/dt-bindings/gpio/gpio.h whenever possible:
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Example of a node using GPIOs:
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@@ -140,6 +131,80 @@ Every GPIO controller node must contain both an empty "gpio-controller"
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property, and a #gpio-cells integer property, which indicates the number of
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cells in a gpio-specifier.
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+Some system-on-chips (SoCs) use the concept of GPIO banks. A GPIO bank is an
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+instance of a hardware IP core on a silicon die, usually exposed to the
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+programmer as a coherent range of I/O addresses. Usually each such bank is
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+exposed in the device tree as an individual gpio-controller node, reflecting
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+the fact that the hardware was synthesized by reusing the same IP block a
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+few times over.
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+
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+Optionally, a GPIO controller may have a "ngpios" property. This property
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+indicates the number of in-use slots of available slots for GPIOs. The
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+typical example is something like this: the hardware register is 32 bits
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+wide, but only 18 of the bits have a physical counterpart. The driver is
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+generally written so that all 32 bits can be used, but the IP block is reused
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+in a lot of designs, some using all 32 bits, some using 18 and some using
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+12. In this case, setting "ngpios = <18>;" informs the driver that only the
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+first 18 GPIOs, at local offset 0 .. 17, are in use.
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+
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+If these GPIOs do not happen to be the first N GPIOs at offset 0...N-1, an
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+additional set of tuples is needed to specify which GPIOs are unusable, with
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+the gpio-reserved-ranges binding. This property indicates the start and size
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+of the GPIOs that can't be used.
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+
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+Optionally, a GPIO controller may have a "gpio-line-names" property. This is
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+an array of strings defining the names of the GPIO lines going out of the
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+GPIO controller. This name should be the most meaningful producer name
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+for the system, such as a rail name indicating the usage. Package names
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+such as pin name are discouraged: such lines have opaque names (since they
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+are by definition generic purpose) and such names are usually not very
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+helpful. For example "MMC-CD", "Red LED Vdd" and "ethernet reset" are
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+reasonable line names as they describe what the line is used for. "GPIO0"
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+is not a good name to give to a GPIO line. Placeholders are discouraged:
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+rather use the "" (blank string) if the use of the GPIO line is undefined
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+in your design. The names are assigned starting from line offset 0 from
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+left to right from the passed array. An incomplete array (where the number
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+of passed named are less than ngpios) will still be used up until the last
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+provided valid line index.
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+
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+Example:
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+
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+gpio-controller@00000000 {
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+ compatible = "foo";
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+ reg = <0x00000000 0x1000>;
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+ gpio-controller;
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+ #gpio-cells = <2>;
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+ ngpios = <18>;
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+ gpio-reserved-ranges = <0 4>, <12 2>;
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+ gpio-line-names = "MMC-CD", "MMC-WP", "VDD eth", "RST eth", "LED R",
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+ "LED G", "LED B", "Col A", "Col B", "Col C", "Col D",
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+ "Row A", "Row B", "Row C", "Row D", "NMI button",
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+ "poweroff", "reset";
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+}
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+
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+The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism
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+providing automatic GPIO request and configuration as part of the
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+gpio-controller's driver probe function.
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+
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+Each GPIO hog definition is represented as a child node of the GPIO controller.
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+Required properties:
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+- gpio-hog: A property specifying that this child node represents a GPIO hog.
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+- gpios: Store the GPIO information (id, flags, ...) for each GPIO to
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+ affect. Shall contain an integer multiple of the number of cells
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+ specified in its parent node (GPIO controller node).
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+Only one of the following properties scanned in the order shown below.
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+This means that when multiple properties are present they will be searched
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+in the order presented below and the first match is taken as the intended
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+configuration.
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+- input: A property specifying to set the GPIO direction as input.
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+- output-low A property specifying to set the GPIO direction as output with
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+ the value low.
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+- output-high A property specifying to set the GPIO direction as output with
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+ the value high.
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+
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+Optional properties:
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+- line-name: The GPIO label name. If not present the node name is used.
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+
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Example of two SOC GPIO banks defined as gpio-controller nodes:
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qe_pio_a: gpio-controller@1400 {
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@@ -161,46 +226,40 @@ Example of two SOC GPIO banks defined as gpio-controller nodes:
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Some or all of the GPIOs provided by a GPIO controller may be routed to pins
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on the package via a pin controller. This allows muxing those pins between
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-GPIO and other functions.
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+GPIO and other functions. It is a fairly common practice among silicon
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+engineers.
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+
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+2.2) Ordinary (numerical) GPIO ranges
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+-------------------------------------
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It is useful to represent which GPIOs correspond to which pins on which pin
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-controllers. The gpio-ranges property described below represents this, and
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-contains information structures as follows:
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-
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- gpio-range-list ::= <single-gpio-range> [gpio-range-list]
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- single-gpio-range ::= <numeric-gpio-range> | <named-gpio-range>
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- numeric-gpio-range ::=
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- <pinctrl-phandle> <gpio-base> <pinctrl-base> <count>
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- named-gpio-range ::= <pinctrl-phandle> <gpio-base> '<0 0>'
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- pinctrl-phandle : phandle to pin controller node
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- gpio-base : Base GPIO ID in the GPIO controller
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- pinctrl-base : Base pinctrl pin ID in the pin controller
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- count : The number of GPIOs/pins in this range
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-
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-The "pin controller node" mentioned above must conform to the bindings
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-described in ../pinctrl/pinctrl-bindings.txt.
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-
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-In case named gpio ranges are used (ranges with both <pinctrl-base> and
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-<count> set to 0), the property gpio-ranges-group-names contains one string
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-for every single-gpio-range in gpio-ranges:
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- gpiorange-names-list ::= <gpiorange-name> [gpiorange-names-list]
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- gpiorange-name : Name of the pingroup associated to the GPIO range in
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- the respective pin controller.
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-
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-Elements of gpiorange-names-list corresponding to numeric ranges contain
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-the empty string. Elements of gpiorange-names-list corresponding to named
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-ranges contain the name of a pin group defined in the respective pin
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-controller. The number of pins/GPIOs in the range is the number of pins in
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-that pin group.
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+controllers. The gpio-ranges property described below represents this with
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+a discrete set of ranges mapping pins from the pin controller local number space
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+to pins in the GPIO controller local number space.
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-Previous versions of this binding required all pin controller nodes that
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-were referenced by any gpio-ranges property to contain a property named
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-#gpio-range-cells with value <3>. This requirement is now deprecated.
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-However, that property may still exist in older device trees for
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-compatibility reasons, and would still be required even in new device
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-trees that need to be compatible with older software.
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+The format is: <[pin controller phandle], [GPIO controller offset],
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+ [pin controller offset], [number of pins]>;
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+
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+The GPIO controller offset pertains to the GPIO controller node containing the
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+range definition.
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+
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+The pin controller node referenced by the phandle must conform to the bindings
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+described in pinctrl/pinctrl-bindings.txt.
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+
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+Each offset runs from 0 to N. It is perfectly fine to pile any number of
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+ranges with just one pin-to-GPIO line mapping if the ranges are concocted, but
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+in practice these ranges are often lumped in discrete sets.
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+
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+Example:
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-Example 1:
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+ gpio-ranges = <&foo 0 20 10>, <&bar 10 50 20>;
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+
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+This means:
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+- pins 20..29 on pin controller "foo" is mapped to GPIO line 0..9 and
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+- pins 50..69 on pin controller "bar" is mapped to GPIO line 10..29
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+
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+
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+Verbose example:
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qe_pio_e: gpio-controller@1460 {
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#gpio-cells = <2>;
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@@ -211,12 +270,33 @@ Example 1:
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};
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Here, a single GPIO controller has GPIOs 0..9 routed to pin controller
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-pinctrl1's pins 20..29, and GPIOs 10..19 routed to pin controller pinctrl2's
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-pins 50..59.
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+pinctrl1's pins 20..29, and GPIOs 10..29 routed to pin controller pinctrl2's
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+pins 50..69.
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+
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+
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+2.3) GPIO ranges from named pin groups
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+--------------------------------------
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-Example 2:
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+It is also possible to use pin groups for gpio ranges when pin groups are the
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+easiest and most convenient mapping.
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- gpio_pio_i: gpio-controller@14B0 {
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+Both both <pinctrl-base> and <count> must set to 0 when using named pin groups
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+names.
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+
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+The property gpio-ranges-group-names must contain exactly one string for each
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+range.
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+
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+Elements of gpio-ranges-group-names must contain the name of a pin group
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+defined in the respective pin controller. The number of pins/GPIO lines in the
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+range is the number of pins in that pin group. The number of pins of that
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+group is defined int the implementation and not in the device tree.
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+
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+If numerical and named pin groups are mixed, the string corresponding to a
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+numerical pin range in gpio-ranges-group-names must be empty.
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+
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+Example:
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+
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+ gpio_pio_i: gpio-controller@14b0 {
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#gpio-cells = <2>;
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compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank";
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reg = <0x1480 0x18>;
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@@ -231,66 +311,14 @@ Example 2:
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"bar";
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};
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-Here, three GPIO ranges are defined wrt. two pin controllers. pinctrl1 GPIO
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-ranges are defined using pin numbers whereas the GPIO ranges wrt. pinctrl2
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-are named "foo" and "bar".
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-
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-3) GPIO hog definitions
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------------------------
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-
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-The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism
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-providing automatic GPIO request and configuration as part of the
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-gpio-controller's driver probe function.
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-
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-Each GPIO hog definition is represented as a child node of the GPIO controller.
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-Required properties:
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-- gpio-hog: A property specifying that this child node represents a GPIO hog.
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-- gpios: Store the GPIO information (id, flags) for the GPIO to
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- affect.
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-
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- ! Not yet support more than one gpio !
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+Here, three GPIO ranges are defined referring to two pin controllers.
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-Only one of the following properties scanned in the order shown below.
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-- input: A property specifying to set the GPIO direction as input.
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-- output-low A property specifying to set the GPIO direction as output with
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- the value low.
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-- output-high A property specifying to set the GPIO direction as output with
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- the value high.
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+pinctrl1 GPIO ranges are defined using pin numbers whereas the GPIO ranges
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+in pinctrl2 are defined using the pin groups named "foo" and "bar".
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-Optional properties:
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-- line-name: The GPIO label name. If not present the node name is used.
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-
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-Example:
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-
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- tca6416@20 {
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- compatible = "ti,tca6416";
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- reg = <0x20>;
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- #gpio-cells = <2>;
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- gpio-controller;
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-
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- env_reset {
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- gpio-hog;
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- input;
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- gpios = <6 GPIO_ACTIVE_LOW>;
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- };
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- boot_rescue {
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- gpio-hog;
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- input;
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- line-name = "foo-bar-gpio";
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- gpios = <7 GPIO_ACTIVE_LOW>;
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- };
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- };
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-
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-For the above Example you can than access the gpio in your boardcode
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-with:
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-
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- struct gpio_desc *desc;
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- int ret;
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-
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- ret = gpio_hog_lookup_name("boot_rescue", &desc);
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- if (ret)
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- return;
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- if (dm_gpio_get_value(desc) == 1)
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- printf("\nBooting into Rescue System\n");
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- else if (dm_gpio_get_value(desc) == 0)
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- printf("\nBoot normal\n");
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+Previous versions of this binding required all pin controller nodes that
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+were referenced by any gpio-ranges property to contain a property named
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+#gpio-range-cells with value <3>. This requirement is now deprecated.
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+However, that property may still exist in older device trees for
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+compatibility reasons, and would still be required even in new device
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+trees that need to be compatible with older software.
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