[PATCH 1/2] spi: dual and quad support(device tree)

[wangyuhang <wangyuhang2014@gmail.com>]

Add spi-tx-nbits and spi-rx-nbits for spi slave node.
 spi-tx-nbits:Number of bits used for MOSI(writting)
 spi-rx-nbits:Number of bits used for MISO(reading)
Support for spi-tx/rx-nbits in SPI framework has been picked[1].
[1]: http://comments.gmane.org/gmane.linux.kernel.spi.devel/14420
Commit Id:f477b7fb13df2b843997559ff34e87d054ba6538

Signed-off-by: wangyuhang <wangyuhang2014@gmail.com>
---
 Documentation/devicetree/bindings/spi/spi-bus.txt |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index 296015e..145ba96 100644
--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
@@ -55,6 +55,20 @@ contain the following properties.
     		chip select active high
 - spi-3wire       - (optional) Empty property indicating device requires
     		    3-wire mode.
+- spi-tx-nbits    - (optional) Number of bits used for MOSI(writting)
+- spi-rx-nbits    - (optional) Number of bits used for MISO(reading)
+
+So if for example the slave has 4 wires for writting and 2 wires for reading,
+and the spi-tx/rx-nbits property should be set as follows:
+
+spi-tx-nbits = <4>;
+spi-rx-nbits = <2>;
+
+Now the value that spi-tx-nbits and spi-rx-nbits can receive is only
+1(single), 2(dual) and 4(quad). If you don't set spi-tx-nbits or spi-rx-nbits,
+spi_device mode will be set in single(1 wire) as default. Another point, if
+property:spi-3wire is set, spi-tx/rx-nbits is forbidden to set to <2 or 4>,
+otherwise, an errro will return.
 
 If a gpio chipselect is used for the SPI slave the gpio number will be passed
 via the cs_gpio
-- 
1.7.9.5


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