[PATCH 3/9] clk: fractional-divider: add CLK_FRAC_DIVIDER_ZERO_BASED flag support

[aisheng.dong@nxp.com (Dong Aisheng)]

Adding CLK_FRAC_DIVIDER_ZERO_BASED flag to indicate the numerator and
denominator value in register are start from 0.

This can be used to support frac dividers like below:
Divider output clock = Divider input clock x [(frac +1) / (div +1)]
where frac/div in register is:
000b - Divide by 1.
001b - Divide by 2.
010b - Divide by 3.

Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Michael Turquette <mturquette@baylibre.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
---
 drivers/clk/clk-fractional-divider.c | 10 ++++++++++
 include/linux/clk-provider.h         |  7 +++++++
 2 files changed, 17 insertions(+)

diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
index aab9046..455bec5 100644
--- a/drivers/clk/clk-fractional-divider.c
+++ b/drivers/clk/clk-fractional-divider.c
@@ -40,6 +40,11 @@ static unsigned long clk_fd_recalc_rate(struct clk_hw *hw,
 	m = (val & fd->mmask) >> fd->mshift;
 	n = (val & fd->nmask) >> fd->nshift;
 
+	if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
+		m++;
+		n++;
+	}
+
 	if (!n || !m)
 		return parent_rate;
 
@@ -91,6 +96,11 @@ static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
 			GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
 			&m, &n);
 
+	if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
+		m--;
+		n--;
+	}
+
 	if (fd->lock)
 		spin_lock_irqsave(fd->lock, flags);
 	else
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index a6efbb9..4466cae 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -557,6 +557,11 @@ void clk_hw_unregister_fixed_factor(struct clk_hw *hw);
  * @lock:	register lock
  *
  * Clock with adjustable fractional divider affecting its output frequency.
+ *
+ * Flags:
+ * CLK_FRAC_DIVIDER_ZERO_BASED - by default the divisor is the value read
+ *	from the register.  If CLK_FRAC_DIVIDER_ZERO_BASED is set then the
+ *	divider is the raw value read from the register plus one.
  */
 struct clk_fractional_divider {
 	struct clk_hw	hw;
@@ -573,6 +578,8 @@ struct clk_fractional_divider {
 
 #define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw)
 
+#define CLK_FRAC_DIVIDER_ZERO_BASED		BIT(0)
+
 extern const struct clk_ops clk_fractional_divider_ops;
 struct clk *clk_register_fractional_divider(struct device *dev,
 		const char *name, const char *parent_name, unsigned long flags,
-- 
2.7.4