linux/Documentation/devicetree/bindings/spi/spi-bus.txt
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   1SPI (Serial Peripheral Interface) busses
   2
   3SPI busses can be described with a node for the SPI master device
   4and a set of child nodes for each SPI slave on the bus.  For this
   5discussion, it is assumed that the system's SPI controller is in
   6SPI master mode.  This binding does not describe SPI controllers
   7in slave mode.
   8
   9The SPI master node requires the following properties:
  10- #address-cells  - number of cells required to define a chip select
  11                address on the SPI bus.
  12- #size-cells     - should be zero.
  13- compatible      - name of SPI bus controller following generic names
  14                recommended practice.
  15- cs-gpios        - (optional) gpios chip select.
  16No other properties are required in the SPI bus node.  It is assumed
  17that a driver for an SPI bus device will understand that it is an SPI bus.
  18However, the binding does not attempt to define the specific method for
  19assigning chip select numbers.  Since SPI chip select configuration is
  20flexible and non-standardized, it is left out of this binding with the
  21assumption that board specific platform code will be used to manage
  22chip selects.  Individual drivers can define additional properties to
  23support describing the chip select layout.
  24
  25Optional property:
  26- num-cs : total number of chipselects
  27
  28If cs-gpios is used the number of chip select will automatically increased
  29with max(cs-gpios > hw cs)
  30
  31So if for example the controller has 2 CS lines, and the cs-gpios
  32property looks like this:
  33
  34cs-gpios = <&gpio1 0 0> <0> <&gpio1 1 0> <&gpio1 2 0>;
  35
  36Then it should be configured so that num_chipselect = 4 with the
  37following mapping:
  38
  39cs0 : &gpio1 0 0
  40cs1 : native
  41cs2 : &gpio1 1 0
  42cs3 : &gpio1 2 0
  43
  44SPI slave nodes must be children of the SPI master node and can
  45contain the following properties.
  46- reg             - (required) chip select address of device.
  47- compatible      - (required) name of SPI device following generic names
  48                recommended practice
  49- spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz
  50- spi-cpol        - (optional) Empty property indicating device requires
  51                inverse clock polarity (CPOL) mode
  52- spi-cpha        - (optional) Empty property indicating device requires
  53                shifted clock phase (CPHA) mode
  54- spi-cs-high     - (optional) Empty property indicating device requires
  55                chip select active high
  56- spi-3wire       - (optional) Empty property indicating device requires
  57                    3-wire mode.
  58
  59If a gpio chipselect is used for the SPI slave the gpio number will be passed
  60via the cs_gpio
  61
  62SPI example for an MPC5200 SPI bus:
  63        spi@f00 {
  64                #address-cells = <1>;
  65                #size-cells = <0>;
  66                compatible = "fsl,mpc5200b-spi","fsl,mpc5200-spi";
  67                reg = <0xf00 0x20>;
  68                interrupts = <2 13 0 2 14 0>;
  69                interrupt-parent = <&mpc5200_pic>;
  70
  71                ethernet-switch@0 {
  72                        compatible = "micrel,ks8995m";
  73                        spi-max-frequency = <1000000>;
  74                        reg = <0>;
  75                };
  76
  77                codec@1 {
  78                        compatible = "ti,tlv320aic26";
  79                        spi-max-frequency = <100000>;
  80                        reg = <1>;
  81                };
  82        };
  83