1 Generic device tree bindings for I2C busses
2 ===========================================
4 This document describes generic bindings which can be used to describe I2C
5 busses and their child devices in a device tree.
7 Required properties (per bus)
8 -----------------------------
10 - #address-cells - should be <1>. Read more about addresses below.
11 - #size-cells - should be <0>.
12 - compatible - name of I2C bus controller
14 For other required properties e.g. to describe register sets,
15 clocks, etc. check the binding documentation of the specific driver.
17 The cells properties above define that an address of children of an I2C bus
18 are described by a single value.
20 Optional properties (per bus)
21 -----------------------------
23 These properties may not be supported by all drivers. However, if a driver
24 wants to support one of the below features, it should adapt these bindings.
27 frequency of bus clock in Hz.
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
37 - i2c-scl-falling-time-ns
38 Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C
41 - i2c-scl-internal-delay-ns
42 Number of nanoseconds the IP core additionally needs to setup SCL.
44 - i2c-scl-rising-time-ns
45 Number of nanoseconds the SCL signal takes to rise; t(r) in the I2C
48 - i2c-sda-falling-time-ns
49 Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C
53 Enable analog filter for i2c lines.
56 Enable digital filter for i2c lines.
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.
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).
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.
75 Required properties (per child device)
76 --------------------------------------
79 name of I2C slave device
82 One or many I2C slave addresses. These are usually a 7 bit addresses.
83 However, flags can be attached to an address. I2C_TEN_BIT_ADDRESS is
84 used to mark a 10 bit address. It is needed to avoid the ambiguity
85 between e.g. a 7 bit address of 0x50 and a 10 bit address of 0x050
86 which, in theory, can be on the same bus.
87 Another flag is I2C_OWN_SLAVE_ADDRESS to mark addresses on which we
88 listen to be devices ourselves.
90 Optional properties (per child device)
91 --------------------------------------
93 These properties may not be supported by all drivers. However, if a driver
94 wants to support one of the below features, it should adapt these bindings.
97 device uses SMBus host notify protocol instead of interrupt line.
100 interrupts used by the device.
103 "irq", "wakeup" and "smbus_alert" names are recognized by I2C core,
104 other names are left to individual drivers.
107 Names of map programmable addresses.
108 It can contain any map needing another address than default one.
111 device can be used as a wakeup source.
113 Binding may contain optional "interrupts" property, describing interrupts
114 used by the device. I2C core will assign "irq" interrupt (or the very first
115 interrupt if not using interrupt names) as primary interrupt for the slave.
117 Alternatively, devices supporting SMBus Host Notify, and connected to
118 adapters that support this feature, may use "host-notify" property. I2C
119 core will create a virtual interrupt for Host Notify and assign it as
120 primary interrupt for the slave.
122 Also, if device is marked as a wakeup source, I2C core will set up "wakeup"
123 interrupt for the device. If "wakeup" interrupt name is not present in the
124 binding, then primary interrupt will be used as wakeup interrupt.