doc: DT: Add Generic Serial Device Tree Bindings

Document a set of generic properties for describing UARTs in a
device tree:
  1. The GPIO modem control properties are currently duplicated across
     hardware-specific binding documentation,
  2. The property for dedicated RTS/CTS hardware flow control lines is
     already supported by several drivers, albeit with a vendor-specific
     prefix, hence make it generic.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <rob@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/devicetree/bindings/serial/serial.txt b/Documentation/devicetree/bindings/serial/serial.txt
new file mode 100644 (file)
index 0000000..fd970f7
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+++ b/Documentation/devicetree/bindings/serial/serial.txt
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+Generic Serial DT Bindings
+
+This document lists a set of generic properties for describing UARTs in a
+device tree.  Whether these properties apply to a particular device depends on
+the DT bindings for the actual device.
+
+Optional properties:
+  - cts-gpios: Must contain a GPIO specifier, referring to the GPIO pin to be
+    used as the UART's CTS line.
+  - dcd-gpios: Must contain a GPIO specifier, referring to the GPIO pin to be
+    used as the UART's DCD line.
+  - dsr-gpios: Must contain a GPIO specifier, referring to the GPIO pin to be
+    used as the UART's DSR line.
+  - dtr-gpios: Must contain a GPIO specifier, referring to the GPIO pin to be
+    used as the UART's DTR line.
+  - rng-gpios: Must contain a GPIO specifier, referring to the GPIO pin to be
+    used as the UART's RNG line.
+  - rts-gpios: Must contain a GPIO specifier, referring to the GPIO pin to be
+    used as the UART's RTS line.
+
+  - uart-has-rtscts: The presence of this property indicates that the
+    UART has dedicated lines for RTS/CTS hardware flow control, and that
+    they are available for use (wired and enabled by pinmux configuration).
+    This depends on both the UART hardware and the board wiring.
+    Note that this property is mutually-exclusive with "cts-gpios" and
+    "rts-gpios" above.
+
+
+Examples:
+
+       uart1: serial@48022000 {
+               compatible = "ti,am3352-uart", "ti,omap3-uart";
+               ti,hwmods = "uart2";
+               clock-frequency = <48000000>;
+               reg = <0x48022000 0x2000>;
+               interrupts = <73>;
+               dmas = <&edma 28 0>, <&edma 29 0>;
+               dma-names = "tx", "rx";
+               dtr-gpios = <&gpio2 22 GPIO_ACTIVE_LOW>;
+               dsr-gpios = <&gpio2 23 GPIO_ACTIVE_LOW>;
+               dcd-gpios = <&gpio2 24 GPIO_ACTIVE_LOW>;
+               rng-gpios = <&gpio2 25 GPIO_ACTIVE_LOW>;
+               cts-gpios = <&gpio0 12 GPIO_ACTIVE_LOW>;
+               rts-gpios = <&gpio0 13 GPIO_ACTIVE_LOW>;
+               status = "okay";
+       };
+
+       scifa4: serial@e6c80000 {
+               compatible = "renesas,scifa-sh73a0", "renesas,scifa";
+               reg = <0xe6c80000 0x100>;
+               interrupts = <GIC_SPI 78 IRQ_TYPE_LEVEL_HIGH>;
+               clocks = <&mstp2_clks SH73A0_CLK_SCIFA4>;
+               clock-names = "fck";
+               power-domains = <&pd_a3sp>;
+               uart-has-rtscts;
+               status = "okay";
+       };