clk: ingenic: Add support for divider tables

Some clocks provided on Ingenic SoCs have dividers, whose hardware value
as written in the register cannot be expressed as an affine function
to the actual divider value.

For instance, for the CPU clock on the JZ4770, the dividers are coded as
follows:

    ------------------
    | Bits     | Div |
    ------------------
    | 0  0  0  |  1  |
    | 0  0  1  |  2  |
    | 0  1  0  |  3  |
    | 0  1  1  |  4  |
    | 1  0  0  |  6  |
    | 1  0  1  |  8  |
    | 1  1  0  | 12  |
    ------------------

To support this setup, we introduce a new field in the
ingenic_cgu_div_info structure that allows to specify the divider table.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/ingenic/cgu.c

@@ -384,8 +384,11 @@ ingenic_clk_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
 		div_reg = readl(cgu->base + clk_info->div.reg);
 		div = (div_reg >> clk_info->div.shift) &
 		      GENMASK(clk_info->div.bits - 1, 0);
-		div += 1;
-		div *= clk_info->div.div;
+
+		if (clk_info->div.div_table)
+			div = clk_info->div.div_table[div];
+		else
+			div = (div + 1) * clk_info->div.div;
 
 		rate /= div;
 	} else if (clk_info->type & CGU_CLK_FIXDIV) {
@@ -395,16 +398,37 @@ ingenic_clk_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
 	return rate;
 }
 
+static unsigned int
+ingenic_clk_calc_hw_div(const struct ingenic_cgu_clk_info *clk_info,
+			unsigned int div)
+{
+	unsigned int i;
+
+	for (i = 0; i < (1 << clk_info->div.bits)
+				&& clk_info->div.div_table[i]; i++) {
+		if (clk_info->div.div_table[i] >= div)
+			return i;
+	}
+
+	return i - 1;
+}
+
 static unsigned
 ingenic_clk_calc_div(const struct ingenic_cgu_clk_info *clk_info,
 		     unsigned long parent_rate, unsigned long req_rate)
 {
-	unsigned div;
+	unsigned int div, hw_div;
 
 	/* calculate the divide */
 	div = DIV_ROUND_UP(parent_rate, req_rate);
 
-	/* and impose hardware constraints */
+	if (clk_info->div.div_table) {
+		hw_div = ingenic_clk_calc_hw_div(clk_info, div);
+
+		return clk_info->div.div_table[hw_div];
+	}
+
+	/* Impose hardware constraints */
 	div = min_t(unsigned, div, 1 << clk_info->div.bits);
 	div = max_t(unsigned, div, 1);
 
@@ -447,7 +471,7 @@ ingenic_clk_set_rate(struct clk_hw *hw, unsigned long req_rate,
 	const struct ingenic_cgu_clk_info *clk_info;
 	const unsigned timeout = 100;
 	unsigned long rate, flags;
-	unsigned div, i;
+	unsigned int hw_div, div, i;
 	u32 reg, mask;
 	int ret = 0;
 
@@ -460,13 +484,18 @@ ingenic_clk_set_rate(struct clk_hw *hw, unsigned long req_rate,
 		if (rate != req_rate)
 			return -EINVAL;
 
+		if (clk_info->div.div_table)
+			hw_div = ingenic_clk_calc_hw_div(clk_info, div);
+		else
+			hw_div = ((div / clk_info->div.div) - 1);
+
 		spin_lock_irqsave(&cgu->lock, flags);
 		reg = readl(cgu->base + clk_info->div.reg);
 
 		/* update the divide */
 		mask = GENMASK(clk_info->div.bits - 1, 0);
 		reg &= ~(mask << clk_info->div.shift);
-		reg |= ((div / clk_info->div.div) - 1) << clk_info->div.shift;
+		reg |= hw_div << clk_info->div.shift;
 
 		/* clear the stop bit */
 		if (clk_info->div.stop_bit != -1)

drivers/clk/ingenic/cgu.h

@@ -88,6 +88,8 @@ struct ingenic_cgu_mux_info {
  *          isn't one
  * @busy_bit: the index of the busy bit within reg, or -1 if there isn't one
  * @stop_bit: the index of the stop bit within reg, or -1 if there isn't one
+ * @div_table: optional table to map the value read from the register to the
+ *             actual divider value
  */
 struct ingenic_cgu_div_info {
 	unsigned reg;
@@ -97,6 +99,7 @@ struct ingenic_cgu_div_info {
 	s8 ce_bit;
 	s8 busy_bit;
 	s8 stop_bit;
+	const u8 *div_table;
 };
 
 /**