diff options
Diffstat (limited to 'dts/Bindings/spi/spi-bus.txt')
| -rw-r--r-- | dts/Bindings/spi/spi-bus.txt | 76 |
1 files changed, 45 insertions, 31 deletions
diff --git a/dts/Bindings/spi/spi-bus.txt b/dts/Bindings/spi/spi-bus.txt index 4b1d6e74c7..1f6e86f787 100644 --- a/dts/Bindings/spi/spi-bus.txt +++ b/dts/Bindings/spi/spi-bus.txt @@ -1,17 +1,23 @@ 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. +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 master node requires the following properties: +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. -- compatible - name of SPI bus controller following generic names - recommended practice. + +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 @@ -21,7 +27,7 @@ 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: +Optional properties (master mode only): - cs-gpios - gpios chip select. - num-cs - total number of chipselects. @@ -41,28 +47,36 @@ 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-lsb-first - (optional) Empty property indicating device requires - LSB first mode. -- spi-tx-bus-width - (optional) The bus width (number of data wires) that is - used for MOSI. Defaults to 1 if not present. -- spi-rx-bus-width - (optional) The bus width (number of data wires) that is - used for MISO. Defaults to 1 if not present. -- spi-rx-delay-us - (optional) Microsecond delay after a read transfer. -- spi-tx-delay-us - (optional) Microsecond delay after a write transfer. + +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 |