dt/bindings/clk: Add PIC32 clock binding documentation.

Document the devicetree bindings for the clock driver found on Microchip
PIC32 class devices.
Signed-off-by: Purna Chandra Mandal <purna.mandal@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Purna Chandra Mandal <purna.mandal@microchip.com>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-clk@vger.kernel.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13246/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

Documentation/devicetree/bindings/clock/microchip,pic32.txt

+Microchip PIC32 Clock Controller Binding
+----------------------------------------
+Microchip clock controller is consists of few oscillators, PLL, multiplexer
+and few divider modules.
+
+This binding uses common clock bindings.
+[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
+
+Required properties:
+- compatible: shall be "microchip,pic32mzda-clk".
+- reg: shall contain base address and length of clock registers.
+- #clock-cells: shall be 1.
+
+Optional properties:
+- microchip,pic32mzda-sosc: shall be added only if platform has
+  secondary oscillator connected.
+
+Example:
+	rootclk: clock-controller@1f801200 {
+		compatible = "microchip,pic32mzda-clk";
+		reg = <0x1f801200 0x200>;
+		#clock-cells = <1>;
+		/* optional */
+		microchip,pic32mzda-sosc;
+	};
+
+
+The clock consumer shall specify the desired clock-output of the clock
+controller (as defined in [2]) by specifying output-id in its "clock"
+phandle cell.
+[2] include/dt-bindings/clock/microchip,pic32-clock.h
+
+For example for UART2:
+uart2: serial@2 {
+	compatible = "microchip,pic32mzda-uart";
+	reg = <>;
+	interrupts = <>;
+	clocks = <&rootclk PB2CLK>;
+};

include/dt-bindings/clock/microchip,pic32-clock.h

+/*
+ * Purna Chandra Mandal,<purna.mandal@microchip.com>
+ * Copyright (C) 2015 Microchip Technology Inc.  All rights reserved.
+ *
+ * This program is free software; you can distribute it and/or modify it
+ * under the terms of the GNU General Public License (Version 2) as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+
+#ifndef _DT_BINDINGS_CLK_MICROCHIP_PIC32_H_
+#define _DT_BINDINGS_CLK_MICROCHIP_PIC32_H_
+
+/* clock output indices */
+#define POSCCLK		0
+#define FRCCLK		1
+#define BFRCCLK		2
+#define LPRCCLK		3
+#define SOSCCLK		4
+#define FRCDIVCLK	5
+#define PLLCLK		6
+#define SCLK		7
+#define PB1CLK		8
+#define PB2CLK		9
+#define PB3CLK		10
+#define PB4CLK		11
+#define PB5CLK		12
+#define PB6CLK		13
+#define PB7CLK		14
+#define REF1CLK		15
+#define REF2CLK		16
+#define REF3CLK		17
+#define REF4CLK		18
+#define REF5CLK		19
+#define UPLLCLK		20
+#define MAXCLKS		21
+
+#endif	/* _DT_BINDINGS_CLK_MICROCHIP_PIC32_H_ */