gpio: SPEAr: add spi chipselect control driver

SPEAr platform provides a provision to control chipselects of ARM PL022
Prime Cell spi controller through its system registers, which otherwise
remains under PL022 control which some protocols do not want.

This commit intends to provide the spi chipselect control in software over
gpiolib interface. spi chip drivers can use the exported gpiolib interface to
define their chipselect through DT or platform data.

Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Shiraz Hashim <shiraz.hashim@st.com>
Reviewed-by: Vipin Kumar <vipin.kumar@st.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 50 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/gpio/spear_spics.txt b/Documentation/devicetree/bindings/gpio/spear_spics.txt
new file mode 100644
index 00000000000..96c37eb1507
--- /dev/null
+++ b/Documentation/devicetree/bindings/gpio/spear_spics.txt
@@ -0,0 +1,50 @@
+=== ST Microelectronics SPEAr SPI CS Driver ===
+
+SPEAr platform provides a provision to control chipselects of ARM PL022 Prime
+Cell spi controller through its system registers, which otherwise remains under
+PL022 control. If chipselect remain under PL022 control then they would be
+released as soon as transfer is over and TxFIFO becomes empty. This is not
+desired by some of the device protocols above spi which expect (multiple)
+transfers without releasing their chipselects.
+
+Chipselects can be controlled by software by turning them as GPIOs. SPEAr
+provides another interface through system registers through which software can
+directly control each PL022 chipselect. Hence, it is natural for SPEAr to export
+the control of this interface as gpio.
+
+Required properties:
+
+  * compatible: should be defined as "st,spear-spics-gpio"
+  * reg: mentioning address range of spics controller
+  * st-spics,peripcfg-reg: peripheral configuration register offset
+  * st-spics,sw-enable-bit: bit offset to enable sw control
+  * st-spics,cs-value-bit: bit offset to drive chipselect low or high
+  * st-spics,cs-enable-mask: chip select number bit mask
+  * st-spics,cs-enable-shift: chip select number program offset
+  * gpio-controller: Marks the device node as gpio controller
+  * #gpio-cells: should be 1 and will mention chip select number
+
+All the above bit offsets are within peripcfg register.
+
+Example:
+-------
+spics: spics@e0700000{
+        compatible = "st,spear-spics-gpio";
+        reg = <0xe0700000 0x1000>;
+        st-spics,peripcfg-reg = <0x3b0>;
+        st-spics,sw-enable-bit = <12>;
+        st-spics,cs-value-bit = <11>;
+        st-spics,cs-enable-mask = <3>;
+        st-spics,cs-enable-shift = <8>;
+        gpio-controller;
+        #gpio-cells = <2>;
+};
+
+
+spi0: spi@e0100000 {
+        status = "okay";
+        num-cs = <3>;
+        cs-gpios = <&gpio1 7 0>, <&spics 0>,
+                   <&spics 1>;
+	...
+}