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spi: Document DT bindings for SPI controllers in slave mode 

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Geert Uytterhoeven 2017-05-22 15:11:40 +02:00 committed by Mark Brown
parent 2ea659a9ef
commit a8830cb19c
1 changed files with 45 additions and 31 deletions
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76
Documentation/devicetree/bindings/spi/spi-bus.txt
View File

@ -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