95 lines
3.4 KiB
Plaintext
Executable file
95 lines
3.4 KiB
Plaintext
Executable file
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 in a device tree.
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Required properties
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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 following generic names
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recommended practice.
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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. This is usually a 7 bit address. However,
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flags can be attached to the address. I2C_TEN_BIT_ADDRESS is used to mark a 10
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bit address. It is needed to avoid the ambiguity between e.g. a 7 bit address
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of 0x50 and a 10 bit address of 0x050 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 listen to
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be devices ourselves.
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Optional properties
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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 the bindings below.
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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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- 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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- host-notify
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device uses SMBus host notify protocol instead of interrupt line.
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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.
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- wakeup-source
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device can be used as a wakeup source.
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- reg
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I2C slave addresses
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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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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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