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 }; 112