148 lines
5.2 KiB
Plaintext
148 lines
5.2 KiB
Plaintext
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Generic device tree bindings for I2C busses
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===========================================
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This document describes generic bindings which can be used to describe I2C
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busses and their child devices in a device tree.
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Required properties (per bus)
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-----------------------------
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- #address-cells - should be <1>. Read more about addresses below.
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- #size-cells - should be <0>.
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- compatible - name of I2C bus controller
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For other required properties e.g. to describe register sets,
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clocks, etc. check the binding documentation of the specific driver.
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The cells properties above define that an address of children of an I2C bus
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are described by a single value.
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Optional properties (per bus)
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-----------------------------
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These properties may not be supported by all drivers. However, if a driver
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wants to support one of the below features, it should adapt these bindings.
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- clock-frequency
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frequency of bus clock in Hz.
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- i2c-bus
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For I2C adapters that have child nodes that are a mixture of both I2C
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devices and non-I2C devices, the 'i2c-bus' subnode can be used for
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populating I2C devices. If the 'i2c-bus' subnode is present, only
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subnodes of this will be considered as I2C slaves. The properties,
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'#address-cells' and '#size-cells' must be defined under this subnode
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if present.
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- i2c-scl-falling-time-ns
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Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C
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specification.
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- i2c-scl-internal-delay-ns
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Number of nanoseconds the IP core additionally needs to setup SCL.
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- i2c-scl-rising-time-ns
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Number of nanoseconds the SCL signal takes to rise; t(r) in the I2C
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specification.
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- i2c-sda-falling-time-ns
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Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C
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specification.
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- i2c-analog-filter
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Enable analog filter for i2c lines.
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- i2c-digital-filter
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Enable digital filter for i2c lines.
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- i2c-digital-filter-width-ns
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Width of spikes which can be filtered by digital filter
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(i2c-digital-filter). This width is specified in nanoseconds.
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- i2c-analog-filter-cutoff-frequency
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Frequency that the analog filter (i2c-analog-filter) uses to distinguish
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which signal to filter. Signal with higher frequency than specified will
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be filtered out. Only lower frequency will pass (this is applicable to
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a low-pass analog filter). Typical value should be above the normal
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i2c bus clock frequency (clock-frequency).
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Specified in Hz.
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- multi-master
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states that there is another master active on this bus. The OS can use
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this information to adapt power management to keep the arbitration awake
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all the time, for example. Can not be combined with 'single-master'.
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- pinctrl
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add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
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recovery, call it "gpio" or "recovery" (deprecated) state
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- scl-gpios
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specify the gpio related to SCL pin. Used for GPIO bus recovery.
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- sda-gpios
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specify the gpio related to SDA pin. Optional for GPIO bus recovery.
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- single-master
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states that there is no other master active on this bus. The OS can use
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this information to detect a stalled bus more reliably, for example.
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Can not be combined with 'multi-master'.
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- smbus
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states that additional SMBus restrictions and features apply to this bus.
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An example of feature is SMBusHostNotify. Examples of restrictions are
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more reserved addresses and timeout definitions.
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- smbus-alert
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states that the optional SMBus-Alert feature apply to this bus.
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Required properties (per child device)
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--------------------------------------
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- compatible
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name of I2C slave device
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- reg
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One or many I2C slave addresses. These are usually a 7 bit addresses.
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However, flags can be attached to an address. I2C_TEN_BIT_ADDRESS is
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used to mark a 10 bit address. It is needed to avoid the ambiguity
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between e.g. a 7 bit address of 0x50 and a 10 bit address of 0x050
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which, in theory, can be on the same bus.
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Another flag is I2C_OWN_SLAVE_ADDRESS to mark addresses on which we
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listen to be devices ourselves.
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Optional properties (per child device)
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--------------------------------------
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These properties may not be supported by all drivers. However, if a driver
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wants to support one of the below features, it should adapt these bindings.
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- host-notify
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device uses SMBus host notify protocol instead of interrupt line.
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- interrupts
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interrupts used by the device.
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- interrupt-names
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"irq", "wakeup" and "smbus_alert" names are recognized by I2C core,
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other names are left to individual drivers.
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- reg-names
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Names of map programmable addresses.
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It can contain any map needing another address than default one.
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- wakeup-source
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device can be used as a wakeup source.
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Binding may contain optional "interrupts" property, describing interrupts
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used by the device. I2C core will assign "irq" interrupt (or the very first
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interrupt if not using interrupt names) as primary interrupt for the slave.
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Alternatively, devices supporting SMBus Host Notify, and connected to
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adapters that support this feature, may use "host-notify" property. I2C
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core will create a virtual interrupt for Host Notify and assign it as
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primary interrupt for the slave.
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Also, if device is marked as a wakeup source, I2C core will set up "wakeup"
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interrupt for the device. If "wakeup" interrupt name is not present in the
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binding, then primary interrupt will be used as wakeup interrupt.
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