[PATCH V2 2/2] spi: dual and quad support(device tree)

[wangyuhang]

Add spi-tmax-nbits and spi-rmax-nbits for spi slave node.
Modify the related dt document(spi-bus.txt)
 spi-tmax-nbits:Max number of bits slave will use for MOSI(writting)
 spi-rmax-nbits:Max number of bits slave will use for MISO(reading)
Support for spi-tx/rmax-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 at gmail.com>
---
 Documentation/devicetree/bindings/spi/spi-bus.txt |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index 296015e..211336c 100644
--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
@@ -55,6 +55,22 @@ contain the following properties.
     		chip select active high
 - spi-3wire       - (optional) Empty property indicating device requires
     		    3-wire mode.
+- spi-tmax-nbits  - (optional) Max number of bits slave will use for
+    		    MOSI(writting)
+- spi-rmax-nbits  - (optional) Max number of bits slave will use 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-tmax-nbits = <4>;
+spi-rmax-nbits = <2>;
+
+Now the value that spi-tmax-nbits and spi-rmax-nbits can receive is only
+1(single), 2(dual) and 4(quad). If you don't set spi-tmax-nbits or spi-rmax-nbits,
+spi_device mode will be set in single(1 wire) as default. Another point, if
+property:spi-3wire is set, spi-t/rmax-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