152 lines
5.3 KiB
Plaintext
152 lines
5.3 KiB
Plaintext
|
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.
|