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1Generic device tree bindings for I2C busses
2===========================================
3
4This document describes generic bindings which can be used to describe I2C
5busses in a device tree.
6
7Required properties
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 following generic names
13 recommended practice.
14
15For other required properties e.g. to describe register sets,
16clocks, etc. check the binding documentation of the specific driver.
17
18The cells properties above define that an address of children of an I2C bus
19are described by a single value. This is usually a 7 bit address. However,
20flags can be attached to the address. I2C_TEN_BIT_ADDRESS is used to mark a 10
21bit address. It is needed to avoid the ambiguity between e.g. a 7 bit address
22of 0x50 and a 10 bit address of 0x050 which, in theory, can be on the same bus.
23Another flag is I2C_OWN_SLAVE_ADDRESS to mark addresses on which we listen to
24be devices ourselves.
25
26Optional properties
27-------------------
28
29These properties may not be supported by all drivers. However, if a driver
30wants to support one of the below features, it should adapt the bindings below.
31
32- clock-frequency
33 frequency of bus clock in Hz.
34
35- i2c-bus
36 For I2C adapters that have child nodes that are a mixture of both I2C
37 devices and non-I2C devices, the 'i2c-bus' subnode can be used for
38 populating I2C devices. If the 'i2c-bus' subnode is present, only
39 subnodes of this will be considered as I2C slaves. The properties,
40 '#address-cells' and '#size-cells' must be defined under this subnode
41 if present.
42
43- i2c-scl-falling-time-ns
44 Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C
45 specification.
46
47- i2c-scl-internal-delay-ns
48 Number of nanoseconds the IP core additionally needs to setup SCL.
49
50- i2c-scl-rising-time-ns
51 Number of nanoseconds the SCL signal takes to rise; t(r) in the I2C
52 specification.
53
54- i2c-sda-falling-time-ns
55 Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C
56 specification.
57
58- i2c-analog-filter
59 Enable analog filter for i2c lines.
60
61- i2c-digital-filter
62 Enable digital filter for i2c lines.
63
64- i2c-digital-filter-width-ns
65 Width of spikes which can be filtered by digital filter
66 (i2c-digital-filter). This width is specified in nanoseconds.
67
68- i2c-analog-filter-cutoff-frequency
69 Frequency that the analog filter (i2c-analog-filter) uses to distinguish
70 which signal to filter. Signal with higher frequency than specified will
71 be filtered out. Only lower frequency will pass (this is applicable to
72 a low-pass analog filter). Typical value should be above the normal
73 i2c bus clock frequency (clock-frequency).
74 Specified in Hz.
75
76- interrupts
77 interrupts used by the device.
78
79- interrupt-names
80 "irq", "wakeup" and "smbus_alert" names are recognized by I2C core,
81 other names are left to individual drivers.
82
83- host-notify
84 device uses SMBus host notify protocol instead of interrupt line.
85
86- multi-master
87 states that there is another master active on this bus. The OS can use
88 this information to adapt power management to keep the arbitration awake
89 all the time, for example.
90
91- wakeup-source
92 device can be used as a wakeup source.
93
94- reg
95 I2C slave addresses
96
97- reg-names
98 Names of map programmable addresses.
99 It can contain any map needing another address than default one.
100
101Binding may contain optional "interrupts" property, describing interrupts
102used by the device. I2C core will assign "irq" interrupt (or the very first
103interrupt if not using interrupt names) as primary interrupt for the slave.
104
105Alternatively, devices supporting SMBus Host Notify, and connected to
106adapters that support this feature, may use "host-notify" property. I2C
107core will create a virtual interrupt for Host Notify and assign it as
108primary interrupt for the slave.
109
110Also, if device is marked as a wakeup source, I2C core will set up "wakeup"
111interrupt for the device. If "wakeup" interrupt name is not present in the
112binding, then primary interrupt will be used as wakeup interrupt.