clk: add fixed rate clock driver

This commit intends to implement "fixed-clock" as in Linux.
(drivers/clk/clk-fixed-rate.c in Linux)

If you need a very simple clock to just provide fixed clock rate
like a crystal oscillator, you do not have to write a new driver.
This driver can support it.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>

drivers/clk/Makefile

@@ -5,7 +5,7 @@
 # SPDX-License-Identifier:      GPL-2.0+
 #
 
-obj-$(CONFIG_CLK) += clk-uclass.o
+obj-$(CONFIG_CLK) += clk-uclass.o clk_fixed_rate.o
 obj-$(CONFIG_ROCKCHIP_RK3036) += clk_rk3036.o
 obj-$(CONFIG_ROCKCHIP_RK3288) += clk_rk3288.o
 obj-$(CONFIG_SANDBOX) += clk_sandbox.o

drivers/clk/clk_fixed_rate.c

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2016 Masahiro Yamada <yamada.masahiro@socionext.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <clk.h>
+#include <dm/device.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+struct clk_fixed_rate {
+	unsigned long fixed_rate;
+};
+
+#define to_clk_fixed_rate(dev)	((struct clk_fixed_rate *)dev_get_platdata(dev))
+
+static ulong clk_fixed_rate_get_rate(struct udevice *dev)
+{
+	return to_clk_fixed_rate(dev)->fixed_rate;
+}
+
+static ulong clk_fixed_rate_get_periph_rate(struct udevice *dev, int periph)
+{
+	return clk_fixed_rate_get_rate(dev);
+}
+
+const struct clk_ops clk_fixed_rate_ops = {
+	.get_rate = clk_fixed_rate_get_rate,
+	.get_periph_rate = clk_fixed_rate_get_periph_rate,
+};
+
+static int clk_fixed_rate_ofdata_to_platdata(struct udevice *dev)
+{
+	to_clk_fixed_rate(dev)->fixed_rate =
+				fdtdec_get_int(gd->fdt_blob, dev->of_offset,
+					       "clock-frequency", 0);
+
+	return 0;
+}
+
+static const struct udevice_id clk_fixed_rate_match[] = {
+	{
+		.compatible = "fixed-clock",
+	},
+	{ /* sentinel */ }
+};
+
+U_BOOT_DRIVER(clk_fixed_rate) = {
+	.name = "fixed_rate_clock",
+	.id = UCLASS_CLK,
+	.of_match = clk_fixed_rate_match,
+	.ofdata_to_platdata = clk_fixed_rate_ofdata_to_platdata,
+	.platdata_auto_alloc_size = sizeof(struct clk_fixed_rate),
+	.ops = &clk_fixed_rate_ops,
+};