clk: Add a basic multiplier clock

Some clocks are using a multiplier component, however, unlike their mux,
gate or divider counterpart, these factors don't have a basic clock
implementation.

This leads to code duplication across platforms that want to use that kind
of clocks, and the impossibility to use the composite clocks with such a
clock without defining your own rate operations.

Create such a driver in order to remove these issues, and hopefully factor
the implementations, reducing code size across platforms and consolidating
the various implementations.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>

include/linux/clk-provider.h

@@ -518,6 +518,48 @@ struct clk *clk_register_fractional_divider(struct device *dev,
 		void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth,
 		u8 clk_divider_flags, spinlock_t *lock);
 
+/**
+ * struct clk_multiplier - adjustable multiplier clock
+ *
+ * @hw:		handle between common and hardware-specific interfaces
+ * @reg:	register containing the multiplier
+ * @shift:	shift to the multiplier bit field
+ * @width:	width of the multiplier bit field
+ * @lock:	register lock
+ *
+ * Clock with an adjustable multiplier affecting its output frequency.
+ * Implements .recalc_rate, .set_rate and .round_rate
+ *
+ * Flags:
+ * CLK_MULTIPLIER_ZERO_BYPASS - By default, the multiplier is the value read
+ *	from the register, with 0 being a valid value effectively
+ *	zeroing the output clock rate. If CLK_MULTIPLIER_ZERO_BYPASS is
+ *	set, then a null multiplier will be considered as a bypass,
+ *	leaving the parent rate unmodified.
+ * CLK_MULTIPLIER_ROUND_CLOSEST - Makes the best calculated divider to be
+ *	rounded to the closest integer instead of the down one.
+ */
+struct clk_multiplier {
+	struct clk_hw	hw;
+	void __iomem	*reg;
+	u8		shift;
+	u8		width;
+	u8		flags;
+	spinlock_t	*lock;
+};
+
+#define CLK_MULTIPLIER_ZERO_BYPASS		BIT(0)
+#define CLK_MULTIPLIER_ROUND_CLOSEST	BIT(1)
+
+extern const struct clk_ops clk_multiplier_ops;
+
+struct clk *clk_register_multiplier(struct device *dev, const char *name,
+				    const char *parent_name,
+				    unsigned long flags,
+				    void __iomem *reg, u8 shift, u8 width,
+				    u8 clk_mult_flags, spinlock_t *lock);
+void clk_unregister_multiplier(struct clk *clk);
+
 /***
  * struct clk_composite - aggregate clock of mux, divider and gate clocks
  *