powerpc/of: added documentation for spi chipselects

Added devicetree binding documentation for gpios used as chipselect. The
code to evaluate these is already present in spi_mpc8xxx.c.

Signed-off-by: Ernst Schwab <eschwab@online.de>
Reviewed-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

diff --git a/Documentation/powerpc/dts-bindings/fsl/spi.txt b/Documentation/powerpc/dts-bindings/fsl/spi.txt
index e7d9a34..80510c0 100644 (file)
--- a/Documentation/powerpc/dts-bindings/fsl/spi.txt
+++ b/Documentation/powerpc/dts-bindings/fsl/spi.txt
@@ -13,6 +13,11 @@ Required properties:
 - interrupt-parent : the phandle for the interrupt controller that
   services interrupts for this device.
 
+Optional properties:
+- gpios : specifies the gpio pins to be used for chipselects.
+  The gpios will be referred to as reg = <index> in the SPI child nodes.
+  If unspecified, a single SPI device without a chip select can be used.
+
 Example:
        spi@4c0 {
                cell-index = <0>;
@@ -21,4 +26,6 @@ Example:
                interrupts = <82 0>;
                interrupt-parent = <700>;
                mode = "cpu";
+               gpios = <&gpio 18 1     // device reg=<0>
+                        &gpio 19 1>;   // device reg=<1>
        };