clk: zynqmp: Fix divider calculation

zynqmp_clk_divider_round_rate() returns actual divider value
after calculating from parent rate and desired rate, even though
that rate is not supported by single divider of hardware. It is
also possible that such divisor value can be achieved through 2
different dividers. As, Linux tries to set such divisor value(out
of range) in single divider set divider is getting failed.

Fix the same by computing best possible combination of two
divisors which provides more accurate clock rate.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Tejas Patel <tejas.patel@xilinx.com>
Signed-off-by: Rajan Vaja <rajan.vaja@xilinx.com>
Link: https://lkml.kernel.org/r/1575527759-26452-6-git-send-email-rajan.vaja@xilinx.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/zynqmp/divider.c

@@ -89,6 +89,42 @@ static unsigned long zynqmp_clk_divider_recalc_rate(struct clk_hw *hw,
 	return DIV_ROUND_UP_ULL(parent_rate, value);
 }
 
+static void zynqmp_get_divider2_val(struct clk_hw *hw,
+				    unsigned long rate,
+				    unsigned long parent_rate,
+				    struct zynqmp_clk_divider *divider,
+				    int *bestdiv)
+{
+	int div1;
+	int div2;
+	long error = LONG_MAX;
+	struct clk_hw *parent_hw = clk_hw_get_parent(hw);
+	struct zynqmp_clk_divider *pdivider = to_zynqmp_clk_divider(parent_hw);
+
+	if (!pdivider)
+		return;
+
+	*bestdiv = 1;
+	for (div1 = 1; div1 <= pdivider->max_div;) {
+		for (div2 = 1; div2 <= divider->max_div;) {
+			long new_error = ((parent_rate / div1) / div2) - rate;
+
+			if (abs(new_error) < abs(error)) {
+				*bestdiv = div2;
+				error = new_error;
+			}
+			if (divider->flags & CLK_DIVIDER_POWER_OF_TWO)
+				div2 = div2 << 1;
+			else
+				div2++;
+		}
+		if (pdivider->flags & CLK_DIVIDER_POWER_OF_TWO)
+			div1 = div1 << 1;
+		else
+			div1++;
+	}
+}
+
 /**
  * zynqmp_clk_divider_round_rate() - Round rate of divider clock
  * @hw:			handle between common and hardware-specific interfaces
@@ -126,6 +162,16 @@ static long zynqmp_clk_divider_round_rate(struct clk_hw *hw,
 
 	bestdiv = zynqmp_divider_get_val(*prate, rate);
 
+	/*
+	 * In case of two divisors, compute best divider values and return
+	 * divider2 value based on compute value. div1 will  be automatically
+	 * set to optimum based on required total divider value.
+	 */
+	if (div_type == TYPE_DIV2 &&
+	    (clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT)) {
+		zynqmp_get_divider2_val(hw, rate, *prate, divider, &bestdiv);
+	}
+
 	if ((clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT) && divider->is_frac)
 		bestdiv = rate % *prate ? 1 : bestdiv;
 	*prate = rate * bestdiv;