gpio/mpc83xx_spisel_boot.c: gpio driver for SPISEL_BOOT signal

Some SoCs in the mpc83xx family, e.g. mpc8309, have a dedicated spi
chip select, SPISEL_BOOT, that is used by the boot code to boot from
flash.

This chip select will typically be used to select a SPI boot
flash. The SPISEL_BOOT signal is controlled by a single bit in the
SPI_CS register.

Implement a gpio driver for the spi chip select register. This allows a
spi driver capable of using gpios as chip select, to bind a chip select
to SPISEL_BOOT.

It may be a little odd to do this as a GPIO driver, since the signal
is neither GP or I, but it is quite convenient to present it to the
spi driver that way. The alternative it to teach mpc8xxx_spi to handle
the SPISEL_BOOT signal itself (that is how it's done in the linux
kernel, see commit 69b921acae8a)

Signed-off-by: Klaus H. Sorensen <khso@prevas.dk>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

1 files changed, 22 insertions, 0 deletions

diff --git a/doc/device-tree-bindings/gpio/fsl,mpc83xx-spisel-boot.txt b/doc/device-tree-bindings/gpio/fsl,mpc83xx-spisel-boot.txt
new file mode 100644
index 00000000000..52d8bb0a5cb
--- /dev/null
+++ b/doc/device-tree-bindings/gpio/fsl,mpc83xx-spisel-boot.txt
@@ -0,0 +1,22 @@
+MPC83xx SPISEL_BOOT gpio controller
+
+Provide access to MPC83xx SPISEL_BOOT signal as a gpio to allow it to be
+easily bound as a SPI controller chip select.
+
+The SPISEL_BOOT signal is always an output.
+
+Required properties:
+
+- compatible: must be "fsl,mpc83xx-spisel-boot" or "fsl,mpc8309-spisel-boot".
+- reg: must point to the SPI_CS register in the SoC register map.
+- ngpios: number of gpios provided by driver, normally 1.
+
+Example:
+
+	spisel_boot: spisel_boot@14c {
+		compatible = "fsl,mpc8309-spisel-boot";
+		reg = <0x14c 0x04>;
+		#gpio-cells = <2>;
+		device_type = "gpio";
+		ngpios = <1>;
+	};