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Diffstat (limited to 'Documentation/devicetree/bindings/gpio/gpio.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/gpio/gpio.txt | 153 |
1 files changed, 119 insertions, 34 deletions
diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt index d933af37069..3fb8f53071b 100644 --- a/Documentation/devicetree/bindings/gpio/gpio.txt +++ b/Documentation/devicetree/bindings/gpio/gpio.txt @@ -13,11 +13,11 @@ properties, each containing a 'gpio-list': gpio-specifier : Array of #gpio-cells specifying specific gpio (controller specific) -GPIO properties should be named "[<name>-]gpios". Exact +GPIO properties should be named "[<name>-]gpios". The exact meaning of each gpios property must be documented in the device tree binding for each device. -For example, the following could be used to describe gpios pins to use +For example, the following could be used to describe GPIO pins used as chip select lines; with chip selects 0, 1 and 3 populated, and chip select 2 left empty: @@ -44,54 +44,126 @@ 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. -Example of the node using GPIOs: +Example of a node using GPIOs: node { gpios = <&qe_pio_e 18 0>; }; In this example gpio-specifier is "18 0" and encodes GPIO pin number, -and empty GPIO flags as accepted by the "qe_pio_e" gpio-controller. +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 both an empty "gpio-controller" -property, and have #gpio-cells contain the size of the gpio-specifier. +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 { - #gpio-cells = <2>; compatible = "fsl,qe-pario-bank-a", "fsl,qe-pario-bank"; reg = <0x1400 0x18>; gpio-controller; + #gpio-cells = <2>; }; 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-cells = <2>; }; -2.1) gpio-controller and pinctrl subsystem ------------------------------------------- - -gpio-controller on a SOC might be tightly coupled with the pinctrl -subsystem, in the sense that the pins can be used by other functions -together with optional gpio feature. - -While the pin allocation is totally managed by the pin ctrl subsystem, -gpio (under gpiolib) is still maintained by gpio drivers. It may happen -that different pin ranges in a SoC is managed by different gpio drivers. - -This makes it logical to let gpio drivers announce their pin ranges to -the pin ctrl subsystem and call 'pinctrl_request_gpio' in order to -request the corresponding pin before any gpio usage. - -For this, the gpio controller can use a pinctrl phandle and pins to -announce the pinrange to the pin ctrl subsystem. For example, +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>; @@ -99,16 +171,29 @@ announce the pinrange to the pin ctrl subsystem. For example, 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. -where, - &pinctrl1 and &pinctrl2 is the phandle to the pinctrl DT node. +Example 2: - Next values specify the base pin and number of pins for the range - handled by 'qe_pio_e' gpio. In the given example from base pin 20 to - pin 29 under pinctrl1 with gpio offset 0 and pin 50 to pin 69 under - pinctrl2 with gpio offset 10 is handled by this gpio controller. + 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"; + }; -The pinctrl node must have "#gpio-range-cells" property to show number of -arguments to pass with phandle from gpio controllers node. +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". |