clk: shmobile: Add DIV6 clock support

DIV6 clocks are divider gate clocks controlled through a single
register. The divider is expressed on 6 bits, hence the name, and can
take values from 1/1 to 1/64.

Those clocks are found on Renesas ARM SoCs.
Signed-off-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: NMike Turquette <mturquette@linaro.org>

Documentation/devicetree/bindings/clock/renesas,cpg-div6-clocks.txt

+* Renesas CPG DIV6 Clock
+
+The CPG DIV6 clocks are variable factor clocks provided by the Clock Pulse
+Generator (CPG). They clock input is divided by a configurable factor from 1
+to 64.
+
+Required Properties:
+
+  - compatible: Must be one of the following
+    - "renesas,r8a7790-div6-clock" for R8A7790 (R-Car H2) DIV6 clocks
+    - "renesas,r8a7791-div6-clock" for R8A7791 (R-Car M2) DIV6 clocks
+    - "renesas,cpg-div6-clock" for generic DIV6 clocks
+  - reg: Base address and length of the memory resource used by the DIV6 clock
+  - clocks: Reference to the parent clock
+  - #clock-cells: Must be 0
+  - clock-output-names: The name of the clock as a free-form string
+
+
+Example
+-------
+
+	sd2_clk: sd2_clk@e6150078 {
+		compatible = "renesas,r8a7790-div6-clock", "renesas,cpg-div6-clock";
+		reg = <0 0xe6150078 0 4>;
+		clocks = <&pll1_div2_clk>;
+		#clock-cells = <0>;
+		clock-output-names = "sd2";
+	};

drivers/clk/shmobile/Makefile

 obj-$(CONFIG_ARCH_R8A7790)		+= clk-rcar-gen2.o
 obj-$(CONFIG_ARCH_R8A7791)		+= clk-rcar-gen2.o
+obj-$(CONFIG_ARCH_SHMOBILE_MULTI)	+= clk-div6.o
 
 # for emply built-in.o
 obj-n	:= dummy

drivers/clk/shmobile/clk-div6.c

+/*
+ * r8a7790 Common Clock Framework support
+ *
+ * Copyright (C) 2013  Renesas Solutions Corp.
+ *
+ * Contact: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ */
+
+#include <linux/clk-provider.h>
+#include <linux/clkdev.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+
+#define CPG_DIV6_CKSTP		BIT(8)
+#define CPG_DIV6_DIV(d)		((d) & 0x3f)
+#define CPG_DIV6_DIV_MASK	0x3f
+
+/**
+ * struct div6_clock - MSTP gating clock
+ * @hw: handle between common and hardware-specific interfaces
+ * @reg: IO-remapped register
+ * @div: divisor value (1-64)
+ */
+struct div6_clock {
+	struct clk_hw hw;
+	void __iomem *reg;
+	unsigned int div;
+};
+
+#define to_div6_clock(_hw) container_of(_hw, struct div6_clock, hw)
+
+static int cpg_div6_clock_enable(struct clk_hw *hw)
+{
+	struct div6_clock *clock = to_div6_clock(hw);
+
+	clk_writel(CPG_DIV6_DIV(clock->div - 1), clock->reg);
+
+	return 0;
+}
+
+static void cpg_div6_clock_disable(struct clk_hw *hw)
+{
+	struct div6_clock *clock = to_div6_clock(hw);
+
+	/* DIV6 clocks require the divisor field to be non-zero when stopping
+	 * the clock.
+	 */
+	clk_writel(CPG_DIV6_CKSTP | CPG_DIV6_DIV(CPG_DIV6_DIV_MASK),
+		   clock->reg);
+}
+
+static int cpg_div6_clock_is_enabled(struct clk_hw *hw)
+{
+	struct div6_clock *clock = to_div6_clock(hw);
+
+	return !(clk_readl(clock->reg) & CPG_DIV6_CKSTP);
+}
+
+static unsigned long cpg_div6_clock_recalc_rate(struct clk_hw *hw,
+						unsigned long parent_rate)
+{
+	struct div6_clock *clock = to_div6_clock(hw);
+	unsigned int div = (clk_readl(clock->reg) & CPG_DIV6_DIV_MASK) + 1;
+
+	return parent_rate / div;
+}
+
+static unsigned int cpg_div6_clock_calc_div(unsigned long rate,
+					    unsigned long parent_rate)
+{
+	unsigned int div;
+
+	div = DIV_ROUND_CLOSEST(parent_rate, rate);
+	return clamp_t(unsigned int, div, 1, 64);
+}
+
+static long cpg_div6_clock_round_rate(struct clk_hw *hw, unsigned long rate,
+				      unsigned long *parent_rate)
+{
+	unsigned int div = cpg_div6_clock_calc_div(rate, *parent_rate);
+
+	return *parent_rate / div;
+}
+
+static int cpg_div6_clock_set_rate(struct clk_hw *hw, unsigned long rate,
+				   unsigned long parent_rate)
+{
+	struct div6_clock *clock = to_div6_clock(hw);
+	unsigned int div = cpg_div6_clock_calc_div(rate, parent_rate);
+
+	clock->div = div;
+
+	/* Only program the new divisor if the clock isn't stopped. */
+	if (!(clk_readl(clock->reg) & CPG_DIV6_CKSTP))
+		clk_writel(CPG_DIV6_DIV(clock->div - 1), clock->reg);
+
+	return 0;
+}
+
+static const struct clk_ops cpg_div6_clock_ops = {
+	.enable = cpg_div6_clock_enable,
+	.disable = cpg_div6_clock_disable,
+	.is_enabled = cpg_div6_clock_is_enabled,
+	.recalc_rate = cpg_div6_clock_recalc_rate,
+	.round_rate = cpg_div6_clock_round_rate,
+	.set_rate = cpg_div6_clock_set_rate,
+};
+
+static void __init cpg_div6_clock_init(struct device_node *np)
+{
+	struct clk_init_data init;
+	struct div6_clock *clock;
+	const char *parent_name;
+	const char *name;
+	struct clk *clk;
+	int ret;
+
+	clock = kzalloc(sizeof(*clock), GFP_KERNEL);
+	if (!clock) {
+		pr_err("%s: failed to allocate %s DIV6 clock\n",
+		       __func__, np->name);
+		return;
+	}
+
+	/* Remap the clock register and read the divisor. Disabling the
+	 * clock overwrites the divisor, so we need to cache its value for the
+	 * enable operation.
+	 */
+	clock->reg = of_iomap(np, 0);
+	if (clock->reg == NULL) {
+		pr_err("%s: failed to map %s DIV6 clock register\n",
+		       __func__, np->name);
+		goto error;
+	}
+
+	clock->div = (clk_readl(clock->reg) & CPG_DIV6_DIV_MASK) + 1;
+
+	/* Parse the DT properties. */
+	ret = of_property_read_string(np, "clock-output-names", &name);
+	if (ret < 0) {
+		pr_err("%s: failed to get %s DIV6 clock output name\n",
+		       __func__, np->name);
+		goto error;
+	}
+
+	parent_name = of_clk_get_parent_name(np, 0);
+	if (parent_name == NULL) {
+		pr_err("%s: failed to get %s DIV6 clock parent name\n",
+		       __func__, np->name);
+		goto error;
+	}
+
+	/* Register the clock. */
+	init.name = name;
+	init.ops = &cpg_div6_clock_ops;
+	init.flags = CLK_IS_BASIC;
+	init.parent_names = &parent_name;
+	init.num_parents = 1;
+
+	clock->hw.init = &init;
+
+	clk = clk_register(NULL, &clock->hw);
+	if (IS_ERR(clk)) {
+		pr_err("%s: failed to register %s DIV6 clock (%ld)\n",
+		       __func__, np->name, PTR_ERR(clk));
+		goto error;
+	}
+
+	of_clk_add_provider(np, of_clk_src_simple_get, clk);
+
+	return;
+
+error:
+	if (clock->reg)
+		iounmap(clock->reg);
+	kfree(clock);
+}
+CLK_OF_DECLARE(cpg_div6_clk, "renesas,cpg-div6-clock", cpg_div6_clock_init);