tjh.dev
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1SPI (Serial Peripheral Interface) busses
2
3SPI busses can be described with a node for the SPI controller device
4and a set of child nodes for each SPI slave on the bus. The system's SPI
5controller may be described for use in SPI master mode or in SPI slave mode,
6but not for both at the same time.
7
8The SPI controller node requires the following properties:
9- compatible - Name of SPI bus controller following generic names
10 recommended practice.
11
12In master mode, the SPI controller node requires the following additional
13properties:
14- #address-cells - number of cells required to define a chip select
15 address on the SPI bus.
16- #size-cells - should be zero.
17
18In slave mode, the SPI controller node requires one additional property:
19- spi-slave - Empty property.
20
21No other properties are required in the SPI bus node. It is assumed
22that a driver for an SPI bus device will understand that it is an SPI bus.
23However, the binding does not attempt to define the specific method for
24assigning chip select numbers. Since SPI chip select configuration is
25flexible and non-standardized, it is left out of this binding with the
26assumption that board specific platform code will be used to manage
27chip selects. Individual drivers can define additional properties to
28support describing the chip select layout.
29
30Optional properties (master mode only):
31- cs-gpios - gpios chip select.
32- num-cs - total number of chipselects.
33
34If cs-gpios is used the number of chip selects will be increased automatically
35with max(cs-gpios > hw cs).
36
37So if for example the controller has 2 CS lines, and the cs-gpios
38property looks like this:
39
40cs-gpios = <&gpio1 0 0>, <0>, <&gpio1 1 0>, <&gpio1 2 0>;
41
42Then it should be configured so that num_chipselect = 4 with the
43following mapping:
44
45cs0 : &gpio1 0 0
46cs1 : native
47cs2 : &gpio1 1 0
48cs3 : &gpio1 2 0
49
50
51SPI slave nodes must be children of the SPI controller node.
52
53In master mode, one or more slave nodes (up to the number of chip selects) can
54be present. Required properties are:
55- compatible - Name of SPI device following generic names recommended
56 practice.
57- reg - Chip select address of device.
58- spi-max-frequency - Maximum SPI clocking speed of device in Hz.
59
60In slave mode, the (single) slave node is optional.
61If present, it must be called "slave". Required properties are:
62- compatible - Name of SPI device following generic names recommended
63 practice.
64
65All slave nodes can contain the following optional properties:
66- spi-cpol - Empty property indicating device requires inverse clock
67 polarity (CPOL) mode.
68- spi-cpha - Empty property indicating device requires shifted clock
69 phase (CPHA) mode.
70- spi-cs-high - Empty property indicating device requires chip select
71 active high.
72- spi-3wire - Empty property indicating device requires 3-wire mode.
73- spi-lsb-first - Empty property indicating device requires LSB first mode.
74- spi-tx-bus-width - The bus width (number of data wires) that is used for MOSI.
75 Defaults to 1 if not present.
76- spi-rx-bus-width - The bus width (number of data wires) that is used for MISO.
77 Defaults to 1 if not present.
78- spi-rx-delay-us - Microsecond delay after a read transfer.
79- spi-tx-delay-us - Microsecond delay after a write transfer.
80
81Some SPI controllers and devices support Dual and Quad SPI transfer mode.
82It allows data in the SPI system to be transferred using 2 wires (DUAL) or 4
83wires (QUAD).
84Now the value that spi-tx-bus-width and spi-rx-bus-width can receive is
85only 1 (SINGLE), 2 (DUAL) and 4 (QUAD).
86Dual/Quad mode is not allowed when 3-wire mode is used.
87
88If a gpio chipselect is used for the SPI slave the gpio number will be passed
89via the SPI master node cs-gpios property.
90
91SPI example for an MPC5200 SPI bus:
92 spi@f00 {
93 #address-cells = <1>;
94 #size-cells = <0>;
95 compatible = "fsl,mpc5200b-spi","fsl,mpc5200-spi";
96 reg = <0xf00 0x20>;
97 interrupts = <2 13 0 2 14 0>;
98 interrupt-parent = <&mpc5200_pic>;
99
100 ethernet-switch@0 {
101 compatible = "micrel,ks8995m";
102 spi-max-frequency = <1000000>;
103 reg = <0>;
104 };
105
106 codec@1 {
107 compatible = "ti,tlv320aic26";
108 spi-max-frequency = <100000>;
109 reg = <1>;
110 };
111 };