Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Reviewed-by: Rob Herring <robh@xxxxxxxxxx>
---
v4:
- Add Reviewed-by,
v3:
- In SPI slave mode, represent the (single) slave device again as a
child of the controller node, which is now optional, and must be
named "slave" if present,
- Split slave node properties in master mode, slave mode, and common
properties,
v2:
- Do not create a child node in SPI slave mode. Instead, add an
"spi-slave" property, and put the mode properties in the controller
node.
---
Documentation/devicetree/bindings/spi/spi-bus.txt | 76 ++++++++++++++---------
1 file changed, 45 insertions(+), 31 deletions(-)
diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index 4b1d6e74c744fe96..1f6e86f787efd229 100644
--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/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
--
2.7.4
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