1Generic device tree bindings for I2C busses 2=========================================== 3 4This document describes generic bindings which can be used to describe I2C 5busses and their child devices in a device tree. 6 7Required properties (per bus) 8----------------------------- 9 10- #address-cells - should be <1>. Read more about addresses below. 11- #size-cells - should be <0>. 12- compatible - name of I2C bus controller 13 14For other required properties e.g. to describe register sets, 15clocks, etc. check the binding documentation of the specific driver. 16 17The cells properties above define that an address of children of an I2C bus 18are described by a single value. 19 20Optional properties (per bus) 21----------------------------- 22 23These properties may not be supported by all drivers. However, if a driver 24wants to support one of the below features, it should adapt these bindings. 25 26- clock-frequency 27 frequency of bus clock in Hz. 28 29- i2c-bus 30 For I2C adapters that have child nodes that are a mixture of both I2C 31 devices and non-I2C devices, the 'i2c-bus' subnode can be used for 32 populating I2C devices. If the 'i2c-bus' subnode is present, only 33 subnodes of this will be considered as I2C slaves. The properties, 34 '#address-cells' and '#size-cells' must be defined under this subnode 35 if present. 36 37- i2c-scl-falling-time-ns 38 Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C 39 specification. 40 41- i2c-scl-internal-delay-ns 42 Number of nanoseconds the IP core additionally needs to setup SCL. 43 44- i2c-scl-rising-time-ns 45 Number of nanoseconds the SCL signal takes to rise; t(r) in the I2C 46 specification. 47 48- i2c-sda-falling-time-ns 49 Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C 50 specification. 51 52- i2c-analog-filter 53 Enable analog filter for i2c lines. 54 55- i2c-digital-filter 56 Enable digital filter for i2c lines. 57 58- i2c-digital-filter-width-ns 59 Width of spikes which can be filtered by digital filter 60 (i2c-digital-filter). This width is specified in nanoseconds. 61 62- i2c-analog-filter-cutoff-frequency 63 Frequency that the analog filter (i2c-analog-filter) uses to distinguish 64 which signal to filter. Signal with higher frequency than specified will 65 be filtered out. Only lower frequency will pass (this is applicable to 66 a low-pass analog filter). Typical value should be above the normal 67 i2c bus clock frequency (clock-frequency). 68 Specified in Hz. 69 70- multi-master 71 states that there is another master active on this bus. The OS can use 72 this information to adapt power management to keep the arbitration awake 73 all the time, for example. Can not be combined with 'single-master'. 74 75- pinctrl 76 add extra pinctrl to configure SCL/SDA pins to GPIO function for bus 77 recovery, call it "gpio" or "recovery" (deprecated) state 78 79- scl-gpios 80 specify the gpio related to SCL pin. Used for GPIO bus recovery. 81 82- sda-gpios 83 specify the gpio related to SDA pin. Optional for GPIO bus recovery. 84 85- single-master 86 states that there is no other master active on this bus. The OS can use 87 this information to detect a stalled bus more reliably, for example. 88 Can not be combined with 'multi-master'. 89 90- smbus 91 states that additional SMBus restrictions and features apply to this bus. 92 An example of feature is SMBusHostNotify. Examples of restrictions are 93 more reserved addresses and timeout definitions. 94 95- smbus-alert 96 states that the optional SMBus-Alert feature apply to this bus. 97 98Required properties (per child device) 99-------------------------------------- 100 101- compatible 102 name of I2C slave device 103 104- reg 105 One or many I2C slave addresses. These are usually a 7 bit addresses. 106 However, flags can be attached to an address. I2C_TEN_BIT_ADDRESS is 107 used to mark a 10 bit address. It is needed to avoid the ambiguity 108 between e.g. a 7 bit address of 0x50 and a 10 bit address of 0x050 109 which, in theory, can be on the same bus. 110 Another flag is I2C_OWN_SLAVE_ADDRESS to mark addresses on which we 111 listen to be devices ourselves. 112 113Optional properties (per child device) 114-------------------------------------- 115 116These properties may not be supported by all drivers. However, if a driver 117wants to support one of the below features, it should adapt these bindings. 118 119- host-notify 120 device uses SMBus host notify protocol instead of interrupt line. 121 122- interrupts 123 interrupts used by the device. 124 125- interrupt-names 126 "irq", "wakeup" and "smbus_alert" names are recognized by I2C core, 127 other names are left to individual drivers. 128 129- reg-names 130 Names of map programmable addresses. 131 It can contain any map needing another address than default one. 132 133- wakeup-source 134 device can be used as a wakeup source. 135 136Binding may contain optional "interrupts" property, describing interrupts 137used by the device. I2C core will assign "irq" interrupt (or the very first 138interrupt if not using interrupt names) as primary interrupt for the slave. 139 140Alternatively, devices supporting SMBus Host Notify, and connected to 141adapters that support this feature, may use "host-notify" property. I2C 142core will create a virtual interrupt for Host Notify and assign it as 143primary interrupt for the slave. 144 145Also, if device is marked as a wakeup source, I2C core will set up "wakeup" 146interrupt for the device. If "wakeup" interrupt name is not present in the 147binding, then primary interrupt will be used as wakeup interrupt. 148