clk: mux: Add support for read-only muxes.

Some platforms have read-only clock muxes that are preconfigured at
reset and cannot be changed at runtime. This patch extends mux clock
driver to allow handling such read-only muxes by adding new
CLK_MUX_READ_ONLY mux flag.
Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

drivers/clk/clk-mux.c

@@ -107,6 +107,11 @@ const struct clk_ops clk_mux_ops = {
 };
 EXPORT_SYMBOL_GPL(clk_mux_ops);
 
+const struct clk_ops clk_mux_ro_ops = {
+	.get_parent = clk_mux_get_parent,
+};
+EXPORT_SYMBOL_GPL(clk_mux_ro_ops);
+
 struct clk *clk_register_mux_table(struct device *dev, const char *name,
 		const char **parent_names, u8 num_parents, unsigned long flags,
 		void __iomem *reg, u8 shift, u32 mask,
@@ -133,7 +138,10 @@ struct clk *clk_register_mux_table(struct device *dev, const char *name,
 	}
 
 	init.name = name;
-	init.ops = &clk_mux_ops;
+	if (clk_mux_flags & CLK_MUX_READ_ONLY)
+		init.ops = &clk_mux_ro_ops;
+	else
+		init.ops = &clk_mux_ops;
 	init.flags = flags | CLK_IS_BASIC;
 	init.parent_names = parent_names;
 	init.num_parents = num_parents;

include/linux/clk-provider.h

@@ -327,8 +327,10 @@ struct clk_mux {
 #define CLK_MUX_INDEX_ONE		BIT(0)
 #define CLK_MUX_INDEX_BIT		BIT(1)
 #define CLK_MUX_HIWORD_MASK		BIT(2)
+#define CLK_MUX_READ_ONLY	BIT(3) /* mux setting cannot be changed */
 
 extern const struct clk_ops clk_mux_ops;
+extern const struct clk_ops clk_mux_ro_ops;
 
 struct clk *clk_register_mux(struct device *dev, const char *name,
 		const char **parent_names, u8 num_parents, unsigned long flags,