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https://github.com/AsahiLinux/u-boot
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94 lines
3.6 KiB
Text
94 lines
3.6 KiB
Text
SPI (Serial Peripheral Interface) busses
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SPI busses can be described with a node for the SPI master device
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and a set of child nodes for each SPI slave on the bus. For this
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discussion, it is assumed that the system's SPI controller is in
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SPI master mode. This binding does not describe SPI controllers
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in slave mode.
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The SPI master node requires the following properties:
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- #address-cells - number of cells required to define a chip select
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address on the SPI bus.
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- #size-cells - should be zero.
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- compatible - name of SPI bus controller following generic names
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recommended practice.
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- cs-gpios - (optional) gpios chip select.
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No other properties are required in the SPI bus node. It is assumed
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that a driver for an SPI bus device will understand that it is an SPI bus.
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However, the binding does not attempt to define the specific method for
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assigning chip select numbers. Since SPI chip select configuration is
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flexible and non-standardized, it is left out of this binding with the
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assumption that board specific platform code will be used to manage
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chip selects. Individual drivers can define additional properties to
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support describing the chip select layout.
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Optional property:
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- num-cs : total number of chipselects
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If cs-gpios is used the number of chip select will automatically increased
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with max(cs-gpios > hw cs)
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So if for example the controller has 2 CS lines, and the cs-gpios
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property looks like this:
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cs-gpios = <&gpio1 0 0> <0> <&gpio1 1 0> <&gpio1 2 0>;
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Then it should be configured so that num_chipselect = 4 with the
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following mapping:
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cs0 : &gpio1 0 0
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cs1 : native
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cs2 : &gpio1 1 0
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cs3 : &gpio1 2 0
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SPI slave nodes must be children of the SPI master node and can
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contain the following properties.
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- reg - (required) chip select address of device.
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- compatible - (required) name of SPI device following generic names
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recommended practice
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- spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz
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- spi-cpol - (optional) Empty property indicating device requires
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inverse clock polarity (CPOL) mode
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- spi-cpha - (optional) Empty property indicating device requires
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shifted clock phase (CPHA) mode
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- spi-cs-high - (optional) Empty property indicating device requires
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chip select active high
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- spi-3wire - (optional) Empty property indicating device requires
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3-wire mode.
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- spi-tx-bus-width - (optional) The bus width(number of data wires) that
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used for MOSI. Defaults to 1 if not present.
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- spi-rx-bus-width - (optional) The bus width(number of data wires) that
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used for MISO. Defaults to 1 if not present.
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- spi-half-duplex - (optional) Indicates that the SPI bus should wait for
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a header byte before reading data from the slave.
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Some SPI controllers and devices support Dual and Quad SPI transfer mode.
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It allows data in SPI system transferred in 2 wires(DUAL) or 4 wires(QUAD).
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Now the value that spi-tx-bus-width and spi-rx-bus-width can receive is
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only 1(SINGLE), 2(DUAL) and 4(QUAD).
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Dual/Quad mode is not allowed when 3-wire mode is used.
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If a gpio chipselect is used for the SPI slave the gpio number will be passed
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via the cs_gpio
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SPI example for an MPC5200 SPI bus:
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spi@f00 {
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#address-cells = <1>;
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#size-cells = <0>;
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compatible = "fsl,mpc5200b-spi","fsl,mpc5200-spi";
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reg = <0xf00 0x20>;
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interrupts = <2 13 0 2 14 0>;
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interrupt-parent = <&mpc5200_pic>;
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ethernet-switch@0 {
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compatible = "micrel,ks8995m";
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spi-max-frequency = <1000000>;
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reg = <0>;
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};
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codec@1 {
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compatible = "ti,tlv320aic26";
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spi-max-frequency = <100000>;
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reg = <1>;
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};
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};
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