Thread (106 messages) 106 messages, 18 authors, 2012-04-11

[PATCH v7 3/3] clk: basic clock hardware types

From: Richard Zhao <hidden>
Date: 2012-03-16 12:26:12
Also in: lkml

[...]
+static int clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate,
+		unsigned long *best_parent_rate)
+{
+	struct clk_divider *divider = to_clk_divider(hw);
+	int i, bestdiv = 0;
+	unsigned long parent_rate, best = 0, now, maxdiv;
+
+	if (!rate)
+		rate = 1;
+
+	maxdiv = (1 << divider->width);
+
+	if (divider->flags & CLK_DIVIDER_ONE_BASED)
+		maxdiv--;
+
+	if (!best_parent_rate) {
+		parent_rate = __clk_get_rate(__clk_get_parent(hw->clk));
+		bestdiv = DIV_ROUND_UP(parent_rate, rate);
+		bestdiv = bestdiv == 0 ? 1 : bestdiv;
+		bestdiv = bestdiv > maxdiv ? maxdiv : bestdiv;
+		return bestdiv;
+	}
+
+	/*
+	 * The maximum divider we can use without overflowing
+	 * unsigned long in rate * i below
+	 */
+	maxdiv = min(ULONG_MAX / rate, maxdiv);
+
+	for (i = 1; i <= maxdiv; i++) {
+		parent_rate = __clk_round_rate(__clk_get_parent(hw->clk),
+				MULT_ROUND_UP(rate, i));
+		now = parent_rate / i;
+		if (now <= rate && now > best) {
+			bestdiv = i;
+			best = now;
+			*best_parent_rate = parent_rate;
Better add		if (now == rate)
				break;
There may be more than one hit for (now == rate). We'd better select
smallest div, thus smallest parent_rate.

It's the same comment for v6, but not show stopper.

Thanks
Richard
+		}
+	}
+
+	if (!bestdiv) {
+		bestdiv = (1 << divider->width);
+		if (divider->flags & CLK_DIVIDER_ONE_BASED)
+			bestdiv--;
+		*best_parent_rate = __clk_round_rate(__clk_get_parent(hw->clk), 1);
+	}
+
+	return bestdiv;
+}
 
Keyboard shortcuts
hback out one level
jnext message in thread
kprevious message in thread
ldrill in
Escclose help / fold thread tree
?toggle this help