[U-Boot] [RFC PATCH 6/6] clk: add fixed rate clock driver

[Masahiro Yamada <yamada.masahiro@socionext.com>]

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.

Note:
As you see in dts/ directories, fixed clocks are often collected in
one container node like this:

  clocks {
          refclk_a: refclk_a {
                  #clock-cells = <0>;
                  compatible = "fixed-clock";
                  clock-frequency = <10000000>;
          };

          refclk_b: refclk_b {
                  #clock-cells = <0>;
                  compatible = "fixed-clock";
                  clock-frequency = <20000000>;
          };
  };

This does not work in the current DM of U-Boot, unfortunately.
The "clocks" node must have 'compatible = "simple-bus";' or something
to bind children.

Most of developers would be unhappy about adding such a compatible
string only in U-Boot because we generally want to use the same set
of device trees beyond projects.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

I do not understand why we need both .get_rate and .get_periph_rate.

I set both in this driver, but I am not sure if I am doing right.


 drivers/clk/Makefile         |  2 +-
 drivers/clk/clk-fixed-rate.c | 58 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 drivers/clk/clk-fixed-rate.c

diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index 5fcdf39..75054db 100644
--- a/drivers/clk/Makefile
+++ b/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-$(CONFIG_$(SPL_)OF_CONTROL) += clk-fdt.o
 obj-$(CONFIG_ROCKCHIP_RK3036) += clk_rk3036.o
 obj-$(CONFIG_ROCKCHIP_RK3288) += clk_rk3288.o
diff --git a/drivers/clk/clk-fixed-rate.c b/drivers/clk/clk-fixed-rate.c
new file mode 100644
index 0000000..048d450
--- /dev/null
+++ b/drivers/clk/clk-fixed-rate.c
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2015 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_priv(dev))
+
+static ulong clk_fixed_get_rate(struct udevice *dev)
+{
+	return to_clk_fixed_rate(dev)->fixed_rate;
+}
+
+static ulong clk_fixed_get_periph_rate(struct udevice *dev, int ignored)
+{
+	return to_clk_fixed_rate(dev)->fixed_rate;
+}
+
+const struct clk_ops clk_fixed_rate_ops = {
+	.get_rate = clk_fixed_get_rate,
+	.get_periph_rate = clk_fixed_get_periph_rate,
+	.get_id = clk_get_id_simple,
+};
+
+static int clk_fixed_rate_probe(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,
+	.probe = clk_fixed_rate_probe,
+	.priv_auto_alloc_size = sizeof(struct clk_fixed_rate),
+	.ops = &clk_fixed_rate_ops,
+};
-- 
1.9.1