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| -rw-r--r-- | Documentation/devicetree/bindings/spi/spi-bus.txt | 111 |
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diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt new file mode 100644 index 000000000..1f6e86f78 --- /dev/null +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt @@ -0,0 +1,111 @@ +SPI (Serial Peripheral Interface) busses + +SPI busses can be described with a node for the SPI controller device +and a set of child nodes for each SPI slave on the bus. The system's SPI +controller may be described for use in SPI master mode or in SPI slave mode, +but not for both at the same time. + +The SPI controller node requires the following properties: +- compatible - Name of SPI bus controller following generic names + recommended practice. + +In master mode, the SPI controller node requires the following additional +properties: +- #address-cells - number of cells required to define a chip select + address on the SPI bus. +- #size-cells - should be zero. + +In slave mode, the SPI controller node requires one additional property: +- spi-slave - Empty property. + +No other properties are required in the SPI bus node. It is assumed +that a driver for an SPI bus device will understand that it is an SPI bus. +However, the binding does not attempt to define the specific method for +assigning chip select numbers. Since SPI chip select configuration is +flexible and non-standardized, it is left out of this binding with the +assumption that board specific platform code will be used to manage +chip selects. Individual drivers can define additional properties to +support describing the chip select layout. + +Optional properties (master mode only): +- cs-gpios - gpios chip select. +- num-cs - total number of chipselects. + +If cs-gpios is used the number of chip selects will be increased automatically +with max(cs-gpios > hw cs). + +So if for example the controller has 2 CS lines, and the cs-gpios +property looks like this: + +cs-gpios = <&gpio1 0 0>, <0>, <&gpio1 1 0>, <&gpio1 2 0>; + +Then it should be configured so that num_chipselect = 4 with the +following mapping: + +cs0 : &gpio1 0 0 +cs1 : native +cs2 : &gpio1 1 0 +cs3 : &gpio1 2 0 + + +SPI slave nodes must be children of the SPI controller node. + +In master mode, one or more slave nodes (up to the number of chip selects) can +be present. Required properties are: +- compatible - Name of SPI device following generic names recommended + practice. +- reg - Chip select address of device. +- spi-max-frequency - Maximum SPI clocking speed of device in Hz. + +In slave mode, the (single) slave node is optional. +If present, it must be called "slave". Required properties are: +- compatible - Name of SPI device following generic names recommended + practice. + +All slave nodes can contain the following optional properties: +- spi-cpol - Empty property indicating device requires inverse clock + polarity (CPOL) mode. +- spi-cpha - Empty property indicating device requires shifted clock + phase (CPHA) mode. +- spi-cs-high - Empty property indicating device requires chip select + active high. +- spi-3wire - Empty property indicating device requires 3-wire mode. +- spi-lsb-first - Empty property indicating device requires LSB first mode. +- spi-tx-bus-width - The bus width (number of data wires) that is used for MOSI. + Defaults to 1 if not present. +- spi-rx-bus-width - The bus width (number of data wires) that is used for MISO. + Defaults to 1 if not present. +- spi-rx-delay-us - Microsecond delay after a read transfer. +- spi-tx-delay-us - Microsecond delay after a write transfer. + +Some SPI controllers and devices support Dual and Quad SPI transfer mode. +It allows data in the SPI system to be transferred using 2 wires (DUAL) or 4 +wires (QUAD). +Now the value that spi-tx-bus-width and spi-rx-bus-width can receive is +only 1 (SINGLE), 2 (DUAL) and 4 (QUAD). +Dual/Quad mode is not allowed when 3-wire mode is used. + +If a gpio chipselect is used for the SPI slave the gpio number will be passed +via the SPI master node cs-gpios property. + +SPI example for an MPC5200 SPI bus: + spi@f00 { + #address-cells = <1>; + #size-cells = <0>; + compatible = "fsl,mpc5200b-spi","fsl,mpc5200-spi"; + reg = <0xf00 0x20>; + interrupts = <2 13 0 2 14 0>; + interrupt-parent = <&mpc5200_pic>; + + ethernet-switch@0 { + compatible = "micrel,ks8995m"; + spi-max-frequency = <1000000>; + reg = <0>; + }; + + codec@1 { + compatible = "ti,tlv320aic26"; + spi-max-frequency = <100000>; + reg = <1>; + }; + }; |