ata: Add DT bindings for the Gemini SATA bridge

This adds device tree bindings for the Cortina Systems Gemini
PATA to SATA bridge.

Cc: [e-mail]
Cc: John Feng-Hsin Chiang <[e-mail]>
Cc: Greentime Hu <[e-mail]>
Acked-by: Hans Ulli Kroll <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

Documentation/devicetree/bindings/ata/cortina,gemini-sata-bridge.txt

···
+* Cortina Systems Gemini SATA Bridge
+
+The Gemini SATA bridge in a SoC-internal PATA to SATA bridge that
+takes two Faraday Technology FTIDE010 PATA controllers and bridges
+them in different configurations to two SATA ports.
+
+Required properties:
+- compatible: should be
+  "cortina,gemini-sata-bridge"
+- reg: registers and size for the block
+- resets: phandles to the reset lines for both SATA bridges
+- reset-names: must be "sata0", "sata1"
+- clocks: phandles to the compulsory peripheral clocks
+- clock-names: must be "SATA0_PCLK", "SATA1_PCLK"
+- syscon: a phandle to the global Gemini system controller
+- cortina,gemini-ata-muxmode: tell the desired multiplexing mode for
+  the ATA controller and SATA bridges. Values 0..3:
+  Mode 0: ata0 master <-> sata0
+          ata1 master <-> sata1
+          ata0 slave interface brought out on IDE pads
+  Mode 1: ata0 master <-> sata0
+          ata1 master <-> sata1
+          ata1 slave interface brought out on IDE pads
+  Mode 2: ata1 master <-> sata1
+          ata1 slave  <-> sata0
+          ata0 master and slave interfaces brought out
+               on IDE pads
+  Mode 3: ata0 master <-> sata0
+          ata0 slave  <-> sata1
+          ata1 master and slave interfaces brought out
+               on IDE pads
+
+Optional boolean properties:
+- cortina,gemini-enable-ide-pins: enables the PATA to IDE connection.
+  The muxmode setting decides whether ATA0 or ATA1 is brought out,
+  and whether master, slave or both interfaces get brought out.
+- cortina,gemini-enable-sata-bridge: enables the PATA to SATA bridge
+  inside the Gemnini SoC. The Muxmode decides what PATA blocks will
+  be muxed out and how.
+
+Example:
+
+sata: sata@46000000 {
+	compatible = "cortina,gemini-sata-bridge";
+	reg = <0x46000000 0x100>;
+	resets = <&rcon 26>, <&rcon 27>;
+	reset-names = "sata0", "sata1";
+	clocks = <&gcc GEMINI_CLK_GATE_SATA0>,
+		 <&gcc GEMINI_CLK_GATE_SATA1>;
+	clock-names = "SATA0_PCLK", "SATA1_PCLK";
+	syscon = <&syscon>;
+	cortina,gemini-ata-muxmode = <3>;
+	cortina,gemini-enable-ide-pins;
+	cortina,gemini-enable-sata-bridge;
+};