clk: add DT clock binding support

Based on work 1st by Ben Herrenschmidt and Jeremy Kerr, then by Grant
Likely, this patch adds support to clk_get to allow drivers to retrieve
clock data from the device tree.

Platforms scan for clocks in DT with of_clk_init and a match table, and
the register a provider through of_clk_add_provider. The provider's
clk_src_get function will be called when a device references the
provider's OF node for a clock reference.

v6 (Rob Herring):
    - Return error values instead of NULL to match clock framework
      expectations

v5 (Rob Herring):
    - Move from drivers/of into common clock subsystem
    - Squashed "dt/clock: add a simple provider get function" and
      "dt/clock: add function to get parent clock name"
    - Rebase to 3.4-rc1
    - Drop CONFIG_OF_CLOCK and just use CONFIG_OF
    - Add missing EXPORT_SYMBOL to various functions
    - s/clock-output-name/clock-output-names/
    - Define that fixed-clock binding is a single output

v4 (Rob Herring):
    - Rework for common clk subsystem
    - Add of_clk_get_parent_name function

v3: - Clarified documentation

v2: - fixed errant ';' causing compile error
    - Editorial fixes from Shawn Guo
    - merged in adding lookup to clkdev
    - changed property names to match established convention. After
      working with the binding a bit it really made more sense to follow the
      lead of 'reg', 'gpios' and 'interrupts' by making the input simply
      'clocks' & 'clock-names' instead of 'clock-input-*', and to only use
      clock-output* for the producer nodes. (Sorry Shawn, this will mean
      you need to change some code, but it should be trivial)
    - Add ability to inherit clocks from parent nodes by using an empty
      'clock-ranges' property.  Useful for busses.  I could use some feedback
      on the new property name, 'clock-ranges' doesn't feel right to me.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Reviewed-by: Shawn Guo <shawn.guo@freescale.com>
Cc: Sascha Hauer <kernel@pengutronix.de>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

include/linux/clk-provider.h

@@ -347,5 +347,19 @@ void __clk_unprepare(struct clk *clk);
 void __clk_reparent(struct clk *clk, struct clk *new_parent);
 unsigned long __clk_round_rate(struct clk *clk, unsigned long rate);
 
+struct of_device_id;
+
+typedef void (*of_clk_init_cb_t)(struct device_node *);
+
+int of_clk_add_provider(struct device_node *np,
+			struct clk *(*clk_src_get)(struct of_phandle_args *args,
+						   void *data),
+			void *data);
+void of_clk_del_provider(struct device_node *np);
+struct clk *of_clk_src_simple_get(struct of_phandle_args *clkspec,
+				  void *data);
+const char *of_clk_get_parent_name(struct device_node *np, int index);
+void of_clk_init(const struct of_device_id *matches);
+
 #endif /* CONFIG_COMMON_CLK */
 #endif /* CLK_PROVIDER_H */

include/linux/clk.h

@@ -310,4 +310,23 @@ struct clk *clk_get_sys(const char *dev_id, const char *con_id);
 int clk_add_alias(const char *alias, const char *alias_dev_name, char *id,
 			struct device *dev);
 
+struct device_node;
+struct of_phandle_args;
+
+#ifdef CONFIG_OF
+struct clk *of_clk_get(struct device_node *np, int index);
+struct clk *of_clk_get_by_name(struct device_node *np, const char *name);
+struct clk *of_clk_get_from_provider(struct of_phandle_args *clkspec);
+#else
+static inline struct clk *of_clk_get(struct device_node *np, int index)
+{
+	return NULL;
+}
+static inline struct clk *of_clk_get_by_name(struct device_node *np,
+					     const char *name)
+{
+	return NULL;
+}
+#endif
+
 #endif