[PATCH v2 2/2] dt-bindings: Add documentation for SPI daisy chain driver.

[Adrian Fiergolski <adrian.fiergolski@fastree3d.com>]

Add documentation for SPI daisy chain driver.

Signed-off-by: Adrian Fiergolski <adrian.fiergolski@fastree3d.com>
---
 .../bindings/spi/spi-daisy_chain.txt          | 56 +++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/spi/spi-daisy_chain.txt

diff --git a/Documentation/devicetree/bindings/spi/spi-daisy_chain.txt b/Documentation/devicetree/bindings/spi/spi-daisy_chain.txt
new file mode 100644
index 000000000000..1e5b046dda83
--- /dev/null
+++ b/Documentation/devicetree/bindings/spi/spi-daisy_chain.txt
@@ -0,0 +1,56 @@
+spi-daisy_chain : The driver handling SPI daisy chains.
+-----------------------------------------------------------
+
+Required properties:
+- compatible		: Should be "spi,daisy_chain"
+- reg			: Chip select assigned to the chain
+
+  For the SPI devices on a common SPI chain - nodes of daisy_chain):
+- spi-daisy-chain-len  : Length (in bytes) of the SPI transfer,
+		         when the SPI device is part of a device chain.
+- spi-daisy-chain-noop : Byte string of no-operation command which should
+		         be send when device is not addressed during the
+			 given SPI transfer
+
+Optional properties:
+  (for the SPI devices on a common SPI chain (nodes of daisy_chain):
+- spi-daisy-chain-bits_per_word : no-operation transfers involve
+                                  one or more words; word sizes like
+				  eight or 12 bits are common.
+				  In-memory wordsizes are powers of two
+				  bytes (e.g. 20 bit samples use 32 bits).
+				  If not defined, it is assumed to be 8.
+
+The daisy chain is a virtual device represented as a regular SPI device. Its
+nodes define physical devices available on the chain. The order of the nodes
+defines the order of the physical devices on the chain: MOSI pin of a device
+represented by the first node is the last one on the MOSI daisy chain. The
+daisy-chain functionality is transparent to the drivers of the physical devices
+on the chain. All nodes share SPI mode, chip select and a max speed of the
+virtual daisy chain device. Once one of the physical devices is being accessed,
+the spi-daisy_chain driver combines this data with no-operation commands of all
+other devices on the chain.
+
+Example:
+
+	daisy_chain0: daisy_chain@0 {
+	        compatible = "spi,daisy_chain";
+		spi-max-frequency = <10000000>;
+		reg = <0>;
+
+		dac0: ltc2632@0 {
+	              compatible = "lltc,ltc2634-l12";
+		      spi-daisy-chain-len = <4>;
+		      spi-daisy-chain-noop = [00 F0 00 00];
+		};
+		dac1: ltc2632@1 {
+	              compatible = "lltc,ltc2634-l12";
+		      spi-daisy-chain-len = <4>;
+		      spi-daisy-chain-noop = [00 F0 00 00];
+		};
+		dac2: ltc2632@2 {
+	              compatible = "lltc,ltc2634-l12";
+		      spi-daisy-chain-len = <4>;
+		      spi-daisy-chain-noop = [00 F0 00 00];
+		};
+	};
-- 
2.27.0