FreeBSD/Linux Kernel Cross Reference
sys/contrib/device-tree/Bindings/i2c/i2c.txt

     Generic device tree bindings for I2C busses
     ===========================================
     
     This document describes generic bindings which can be used to describe I2C
     busses and their child devices in a device tree.
     
     Required properties (per bus)
     -----------------------------
     
    - #address-cells  - should be <1>. Read more about addresses below.
    - #size-cells     - should be <0>.
    - compatible      - name of I2C bus controller
    
    For other required properties e.g. to describe register sets,
    clocks, etc. check the binding documentation of the specific driver.
    
    The cells properties above define that an address of children of an I2C bus
    are described by a single value.
    
    Optional properties (per bus)
    -----------------------------
    
    These properties may not be supported by all drivers. However, if a driver
    wants to support one of the below features, it should adapt these bindings.
    
    - clock-frequency
            frequency of bus clock in Hz.
    
    - i2c-bus
            For I2C adapters that have child nodes that are a mixture of both I2C
            devices and non-I2C devices, the 'i2c-bus' subnode can be used for
            populating I2C devices. If the 'i2c-bus' subnode is present, only
            subnodes of this will be considered as I2C slaves. The properties,
            '#address-cells' and '#size-cells' must be defined under this subnode
            if present.
    
    - i2c-scl-falling-time-ns
            Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C
            specification.
    
    - i2c-scl-internal-delay-ns
            Number of nanoseconds the IP core additionally needs to setup SCL.
    
    - i2c-scl-rising-time-ns
            Number of nanoseconds the SCL signal takes to rise; t(r) in the I2C
            specification.
    
    - i2c-sda-falling-time-ns
            Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C
            specification.
    
    - i2c-analog-filter
            Enable analog filter for i2c lines.
    
    - i2c-digital-filter
            Enable digital filter for i2c lines.
    
    - i2c-digital-filter-width-ns
            Width of spikes which can be filtered by digital filter
            (i2c-digital-filter). This width is specified in nanoseconds.
    
    - i2c-analog-filter-cutoff-frequency
            Frequency that the analog filter (i2c-analog-filter) uses to distinguish
            which signal to filter. Signal with higher frequency than specified will
            be filtered out. Only lower frequency will pass (this is applicable to
            a low-pass analog filter). Typical value should be above the normal
            i2c bus clock frequency (clock-frequency).
            Specified in Hz.
    
    - multi-master
            states that there is another master active on this bus. The OS can use
            this information to adapt power management to keep the arbitration awake
            all the time, for example. Can not be combined with 'single-master'.
    
    - pinctrl
            add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
            recovery, call it "gpio" or "recovery" (deprecated) state
    
    - scl-gpios
            specify the gpio related to SCL pin. Used for GPIO bus recovery.
    
    - sda-gpios
            specify the gpio related to SDA pin. Optional for GPIO bus recovery.
    
    - single-master
            states that there is no other master active on this bus. The OS can use
            this information to detect a stalled bus more reliably, for example.
            Can not be combined with 'multi-master'.
    
    - smbus
            states that additional SMBus restrictions and features apply to this bus.
            An example of feature is SMBusHostNotify. Examples of restrictions are
            more reserved addresses and timeout definitions.
    
    - smbus-alert
            states that the optional SMBus-Alert feature apply to this bus.
    
    - mctp-controller
            indicates that the system is accessible via this bus as an endpoint for
           MCTP over I2C transport.
   
   Required properties (per child device)
   --------------------------------------
   
   - compatible
           name of I2C slave device
   
   - reg
           One or many I2C slave addresses. These are usually a 7 bit addresses.
           However, flags can be attached to an address. I2C_TEN_BIT_ADDRESS is
           used to mark a 10 bit address. It is needed to avoid the ambiguity
           between e.g. a 7 bit address of 0x50 and a 10 bit address of 0x050
           which, in theory, can be on the same bus.
           Another flag is I2C_OWN_SLAVE_ADDRESS to mark addresses on which we
           listen to be devices ourselves.
   
   Optional properties (per child device)
   --------------------------------------
   
   These properties may not be supported by all drivers. However, if a driver
   wants to support one of the below features, it should adapt these bindings.
   
   - host-notify
           device uses SMBus host notify protocol instead of interrupt line.
   
   - interrupts
           interrupts used by the device.
   
   - interrupt-names
           "irq", "wakeup" and "smbus_alert" names are recognized by I2C core,
           other names are left to individual drivers.
   
   - reg-names
           Names of map programmable addresses.
           It can contain any map needing another address than default one.
   
   - wakeup-source
           device can be used as a wakeup source.
   
   Binding may contain optional "interrupts" property, describing interrupts
   used by the device. I2C core will assign "irq" interrupt (or the very first
   interrupt if not using interrupt names) as primary interrupt for the slave.
   
   Alternatively, devices supporting SMBus Host Notify, and connected to
   adapters that support this feature, may use "host-notify" property. I2C
   core will create a virtual interrupt for Host Notify and assign it as
   primary interrupt for the slave.
   
   Also, if device is marked as a wakeup source, I2C core will set up "wakeup"
   interrupt for the device. If "wakeup" interrupt name is not present in the
   binding, then primary interrupt will be used as wakeup interrupt.

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