spi: davinci: add support for adding delay between word's transmissions

This patch adds ability to configure delay between transmission of
words over SPI bus if it's required by SPI slave devices.

New optional SPI slave property:
- ti,spi-word-delay : delay between transmission of words
	(SPIFMTn.WDELAY, SPIDAT1.WDEL)

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/spi/spi-davinci.txt b/Documentation/devicetree/bindings/spi/spi-davinci.txt
index f80887bca0d6..12ecfe9e3599 100644
--- a/Documentation/devicetree/bindings/spi/spi-davinci.txt
+++ b/Documentation/devicetree/bindings/spi/spi-davinci.txt
@@ -1,5 +1,10 @@
 Davinci SPI controller device bindings
 
+Links on DM:
+Keystone 2 - http://www.ti.com/lit/ug/sprugp2a/sprugp2a.pdf
+dm644x - http://www.ti.com/lit/ug/sprue32a/sprue32a.pdf
+OMAP-L138/da830 - http://www.ti.com/lit/ug/spruh77a/spruh77a.pdf
+
 Required properties:
 - #address-cells: number of cells required to define a chip select
 	address on the SPI bus. Should be set to 1.
@@ -24,6 +29,30 @@ Optional:
 	cs-gpios = <0>, <0>, <0>, <&gpio1 30 0>, <&gpio1 31 0>;
 	where first three are internal CS and last two are GPIO CS.
 
+Optional properties for slave devices:
+SPI slave nodes can contain the following properties.
+Not all SPI Peripherals from Texas Instruments support this.
+Please check SPI peripheral documentation for a device before using these.
+
+- ti,spi-wdelay : delay between transmission of words
+	(SPIFMTn.WDELAY, SPIDAT1.WDEL) must be specified in number of SPI module
+	clock periods.
+
+	delay = WDELAY * SPI_module_clock_period + 2 * SPI_module_clock_period
+
+Below is timing diagram which shows functional meaning of
+"ti,spi-wdelay" parameter.
+
+             +-+ +-+ +-+ +-+ +-+                           +-+ +-+ +-+
+SPI_CLK      | | | | | | | | | |                           | | | | | |
+  +----------+ +-+ +-+ +-+ +-+ +---------------------------+ +-+ +-+ +-
+
+SPI_SOMI/SIMO+-----------------+                           +-----------
+  +----------+ word1           +---------------------------+word2
+             +-----------------+                           +-----------
+                                          WDELAY
+                                <-------------------------->
+
 Example of a NOR flash slave device (n25q032) connected to DaVinci
 SPI controller device over the SPI bus.
 
@@ -43,6 +72,7 @@ spi0:spi@20BF0000 {
 		compatible = "st,m25p32";
 		spi-max-frequency = <25000000>;
 		reg = <0>;
+		ti,spi-wdelay = <8>;
 
 		partition@0 {
 			label = "u-boot-spl";