FreeBSD/Linux Kernel Cross Reference
sys/contrib/device-tree/Bindings/pinctrl/sprd,pinctrl.txt

     * Spreadtrum Pin Controller
     
     The Spreadtrum pin controller are organized in 3 blocks (types).
     
     The first block comprises some global control registers, and each
     register contains several bit fields with one bit or several bits
     to configure for some global common configuration, such as domain
     pad driving level, system control select and so on ("domain pad
     driving level": One pin can output 3.0v or 1.8v, depending on the
    related domain pad driving selection, if the related domain pad
    slect 3.0v, then the pin can output 3.0v. "system control" is used
    to choose one function (like: UART0) for which system, since we
    have several systems (AP/CP/CM4) on one SoC.).
    
    There are too much various configuration that we can not list all
    of them, so we can not make every Spreadtrum-special configuration
    as one generic configuration, and maybe it will add more strange
    global configuration in future. Then we add one "sprd,control" to
    set these various global control configuration, and we need use
    magic number for this property.
    
    Moreover we recognise every fields comprising one bit or several
    bits in one global control register as one pin, thus we should
    record every pin's bit offset, bit width and register offset to
    configure this field (pin).
    
    The second block comprises some common registers which have unified
    register definition, and each register described one pin is used
    to configure the pin sleep mode, function select and sleep related
    configuration.
    
    Now we have 4 systems for sleep mode on SC9860 SoC: AP system,
    PUBCP system, TGLDSP system and AGDSP system. And the pin sleep
    related configuration are:
    - input-enable
    - input-disable
    - output-high
    - output-low
    - bias-pull-up
    - bias-pull-down
    
    In some situation we need set the pin sleep mode and pin sleep related
    configuration, to set the pin sleep related configuration automatically
    by hardware when the system specified by sleep mode goes into deep
    sleep mode. For example, if we set the pin sleep mode as PUBCP_SLEEP
    and set the pin sleep related configuration as "input-enable", which
    means when PUBCP system goes into deep sleep mode, this pin will be set
    input enable automatically.
    
    Moreover we can not use the "sleep" state, since some systems (like:
    PUBCP system) do not run linux kernel OS (only AP system run linux
    kernel on SC9860 platform), then we can not select "sleep" state
    when the PUBCP system goes into deep sleep mode. Thus we introduce
    "sprd,sleep-mode" property to set pin sleep mode.
    
    The last block comprises some misc registers which also have unified
    register definition, and each register described one pin is used to
    configure drive strength, pull up/down and so on. Especially for pull
    up, we have two kind pull up resistor: 20K and 4.7K.
    
    Required properties for Spreadtrum pin controller:
    - compatible: "sprd,<soc>-pinctrl"
      Please refer to each sprd,<soc>-pinctrl.txt binding doc for supported SoCs.
    - reg: The register address of pin controller device.
    - pins : An array of pin names.
    
    Optional properties:
    - function: Specified the function name.
    - drive-strength: Drive strength in mA.
    - input-schmitt-disable: Enable schmitt-trigger mode.
    - input-schmitt-enable: Disable schmitt-trigger mode.
    - bias-disable: Disable pin bias.
    - bias-pull-down: Pull down on pin.
    - bias-pull-up: Pull up on pin.
    - input-enable: Enable pin input.
    - input-disable: Enable pin output.
    - output-high: Set the pin as an output level high.
    - output-low: Set the pin as an output level low.
    - sleep-hardware-state: Indicate these configs in this state are sleep related.
    - sprd,control: Control values referring to databook for global control pins.
    - sprd,sleep-mode: Sleep mode selection.
    
    Please refer to each sprd,<soc>-pinctrl.txt binding doc for supported values.

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