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| -rw-r--r-- | doc/device-tree-bindings/spi/spi-bus.txt | 92 |
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diff --git a/doc/device-tree-bindings/spi/spi-bus.txt b/doc/device-tree-bindings/spi/spi-bus.txt new file mode 100644 index 0000000000..800dafe5b0 --- /dev/null +++ b/doc/device-tree-bindings/spi/spi-bus.txt @@ -0,0 +1,92 @@ +SPI (Serial Peripheral Interface) busses + +SPI busses can be described with a node for the SPI master device +and a set of child nodes for each SPI slave on the bus. For this +discussion, it is assumed that the system's SPI controller is in +SPI master mode. This binding does not describe SPI controllers +in slave mode. + +The SPI master node requires the following properties: +- #address-cells - number of cells required to define a chip select + address on the SPI bus. +- #size-cells - should be zero. +- compatible - name of SPI bus controller following generic names + recommended practice. +- cs-gpios - (optional) gpios chip select. +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 property: +- num-cs : total number of chipselects + +If cs-gpios is used the number of chip select will automatically increased +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 master node and can +contain the following properties. +- reg - (required) chip select address of device. +- compatible - (required) name of SPI device following generic names + recommended practice +- spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz +- spi-cpol - (optional) Empty property indicating device requires + inverse clock polarity (CPOL) mode +- spi-cpha - (optional) Empty property indicating device requires + shifted clock phase (CPHA) mode +- spi-cs-high - (optional) Empty property indicating device requires + chip select active high +- spi-3wire - (optional) Empty property indicating device requires + 3-wire mode. +- spi-tx-bus-width - (optional) The bus width(number of data wires) that + used for MOSI. Defaults to 1 if not present. +- spi-rx-bus-width - (optional) The bus width(number of data wires) that + used for MISO. Defaults to 1 if not present. + +Some SPI controllers and devices support Dual and Quad SPI transfer mode. +It allows data in SPI system transfered in 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 cs_gpio + +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>; + }; + }; |