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.