clk: fixed: Add comment to clk_fixed_set_rate

Currently it is not made explicit why clk_fixed_set_rate() can ignore
its arguments and unconditionally return success. Add a comment
to explain this.

We also mark the clk_ops table const since it should never be
modified at runtime.
Suggested-by: NStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: NDaniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: NStephen Boyd <sboyd@codeaurora.org>

drivers/clk/clk-fixed-factor.c

@@ -55,10 +55,16 @@ static long clk_factor_round_rate(struct clk_hw *hw, unsigned long rate,
 static int clk_factor_set_rate(struct clk_hw *hw, unsigned long rate,
 				unsigned long parent_rate)
 {
+	/*
+	 * We must report success but we can do so unconditionally because
+	 * clk_factor_round_rate returns values that ensure this call is a
+	 * nop.
+	 */
+
 	return 0;
 }
 
-struct clk_ops clk_fixed_factor_ops = {
+const struct clk_ops clk_fixed_factor_ops = {
 	.round_rate = clk_factor_round_rate,
 	.set_rate = clk_factor_set_rate,
 	.recalc_rate = clk_factor_recalc_rate,

include/linux/clk-provider.h

@@ -459,7 +459,7 @@ struct clk_fixed_factor {
 	unsigned int	div;
 };
 
-extern struct clk_ops clk_fixed_factor_ops;
+extern const struct clk_ops clk_fixed_factor_ops;
 struct clk *clk_register_fixed_factor(struct device *dev, const char *name,
 		const char *parent_name, unsigned long flags,
 		unsigned int mult, unsigned int div);