mirror of https://gitee.com/openkylin/linux.git
141 lines
4.6 KiB
Plaintext
141 lines
4.6 KiB
Plaintext
Generic device tree bindings for I3C busses
|
|
===========================================
|
|
|
|
This document describes generic bindings that should be used to describe I3C
|
|
busses in a device tree.
|
|
|
|
Required properties
|
|
-------------------
|
|
|
|
- #address-cells - should be <3>. Read more about addresses below.
|
|
- #size-cells - should be <0>.
|
|
- compatible - name of the I3C master controller driving the I3C bus
|
|
|
|
For other required properties e.g. to describe register sets,
|
|
clocks, etc. check the binding documentation of the specific driver.
|
|
The node describing an I3C bus should be named i3c-master.
|
|
|
|
Optional properties
|
|
-------------------
|
|
|
|
These properties may not be supported by all I3C master drivers. Each I3C
|
|
master bindings should specify which of them are supported.
|
|
|
|
- i3c-scl-hz: frequency of the SCL signal used for I3C transfers.
|
|
When undefined the core sets it to 12.5MHz.
|
|
|
|
- i2c-scl-hz: frequency of the SCL signal used for I2C transfers.
|
|
When undefined, the core looks at LVR (Legacy Virtual Register)
|
|
values of I2C devices described in the device tree to determine
|
|
the maximum I2C frequency.
|
|
|
|
I2C devices
|
|
===========
|
|
|
|
Each I2C device connected to the bus should be described in a subnode. All
|
|
properties described in Documentation/devicetree/bindings/i2c/i2c.txt are
|
|
valid here, but several new properties have been added.
|
|
|
|
New constraint on existing properties:
|
|
--------------------------------------
|
|
- reg: contains 3 cells
|
|
+ first cell : still encoding the I2C address. 10 bit addressing is not
|
|
supported. Devices with 10 bit address can't be properly passed through
|
|
DEFSLVS command.
|
|
|
|
+ second cell: shall be 0
|
|
|
|
+ third cell: shall encode the I3C LVR (Legacy Virtual Register)
|
|
bit[31:8]: unused/ignored
|
|
bit[7:5]: I2C device index. Possible values
|
|
* 0: I2C device has a 50 ns spike filter
|
|
* 1: I2C device does not have a 50 ns spike filter but supports high
|
|
frequency on SCL
|
|
* 2: I2C device does not have a 50 ns spike filter and is not tolerant
|
|
to high frequencies
|
|
* 3-7: reserved
|
|
|
|
bit[4]: tell whether the device operates in FM (Fast Mode) or FM+ mode
|
|
* 0: FM+ mode
|
|
* 1: FM mode
|
|
|
|
bit[3:0]: device type
|
|
* 0-15: reserved
|
|
|
|
The I2C node unit-address should always match the first cell of the reg
|
|
property: <device-type>@<i2c-address>.
|
|
|
|
I3C devices
|
|
===========
|
|
|
|
All I3C devices are supposed to support DAA (Dynamic Address Assignment), and
|
|
are thus discoverable. So, by default, I3C devices do not have to be described
|
|
in the device tree.
|
|
This being said, one might want to attach extra resources to these devices,
|
|
and those resources may have to be described in the device tree, which in turn
|
|
means we have to describe I3C devices.
|
|
|
|
Another use case for describing an I3C device in the device tree is when this
|
|
I3C device has a static I2C address and we want to assign it a specific I3C
|
|
dynamic address before the DAA takes place (so that other devices on the bus
|
|
can't take this dynamic address).
|
|
|
|
The I3C device should be names <device-type>@<static-i2c-address>,<i3c-pid>,
|
|
where device-type is describing the type of device connected on the bus
|
|
(gpio-controller, sensor, ...).
|
|
|
|
Required properties
|
|
-------------------
|
|
- reg: contains 3 cells
|
|
+ first cell : encodes the static I2C address. Should be 0 if the device does
|
|
not have one (0 is not a valid I2C address).
|
|
|
|
+ second and third cells: should encode the ProvisionalID. The second cell
|
|
contains the manufacturer ID left-shifted by 1.
|
|
The third cell contains ORing of the part ID
|
|
left-shifted by 16, the instance ID left-shifted
|
|
by 12 and the extra information. This encoding is
|
|
following the PID definition provided by the I3C
|
|
specification.
|
|
|
|
Optional properties
|
|
-------------------
|
|
- assigned-address: dynamic address to be assigned to this device. This
|
|
property is only valid if the I3C device has a static
|
|
address (first cell of the reg property != 0).
|
|
|
|
|
|
Example:
|
|
|
|
i3c-master@d040000 {
|
|
compatible = "cdns,i3c-master";
|
|
clocks = <&coreclock>, <&i3csysclock>;
|
|
clock-names = "pclk", "sysclk";
|
|
interrupts = <3 0>;
|
|
reg = <0x0d040000 0x1000>;
|
|
#address-cells = <3>;
|
|
#size-cells = <0>;
|
|
i2c-scl-hz = <100000>;
|
|
|
|
/* I2C device. */
|
|
nunchuk: nunchuk@52 {
|
|
compatible = "nintendo,nunchuk";
|
|
reg = <0x52 0x0 0x10>;
|
|
};
|
|
|
|
/* I3C device with a static I2C address. */
|
|
thermal_sensor: sensor@68,39200144004 {
|
|
reg = <0x68 0x392 0x144004>;
|
|
assigned-address = <0xa>;
|
|
};
|
|
|
|
/*
|
|
* I3C device without a static I2C address but requiring
|
|
* resources described in the DT.
|
|
*/
|
|
sensor@0,39200154004 {
|
|
reg = <0x0 0x392 0x154004>;
|
|
clocks = <&clock_provider 0>;
|
|
};
|
|
};
|