Commit 7e50e7e1 authored Feb 13, 2014 by Tomi Valkeinen Committed by Mike Turquette Feb 26, 2014

clk: ti/divider: fix rate calculation for fractional rates



ti/clk-divider.c does not calculate the rates consistently at the moment.

As an example, on OMAP3 we have a clock divider with a source clock of
864000000 Hz. With dividers 6, 7 and 8 the theoretical rates are:

6: 144000000
7: 123428571.428571...
8: 108000000

Calling clk_round_rate() with the rate in the first column will give the
rate in the second column:

144000000 -> 144000000
143999999 -> 123428571
123428572 -> 123428571
123428571 -> 108000000

Note how clk_round_rate() returns 123428571 for rates from 123428572 to
143999999, which is mathematically correct, but when clk_round_rate() is
called with 123428571, the returned value is surprisingly 108000000.

This means that the following code works a bit oddly:

rate = clk_round_rate(clk, 123428572);
clk_set_rate(clk, rate);

As clk_set_rate() also does clock rate rounding, the result is that the
clock is set to the rate of 108000000, not 123428571 returned by the
clk_round_rate.

This patch changes the ti/clk-divider.c to use DIV_ROUND_UP when
calculating the rate. This gives the following behavior which fixes the
inconsistency:

144000000 -> 144000000
143999999 -> 123428572
123428572 -> 123428572
123428571 -> 108000000

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

parent b11d282d

drivers/clk/ti/divider.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -112,7 +112,7 @@ static unsigned long ti_clk_divider_recalc_rate(struct clk_hw *hw,
		return parent_rate;
		}

		return parent_rate / div;
		return DIV_ROUND_UP(parent_rate, div);
		}

		/*
		@@ -182,7 +182,7 @@ static int ti_clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate,
		}
		parent_rate = __clk_round_rate(__clk_get_parent(hw->clk),
		MULT_ROUND_UP(rate, i));
		now = parent_rate / i;
		now = DIV_ROUND_UP(parent_rate, i);
		if (now <= rate && now > best) {
		bestdiv = i;
		best = now;
		@@ -205,7 +205,7 @@ static long ti_clk_divider_round_rate(struct clk_hw *hw, unsigned long rate,
		int div;
		div = ti_clk_divider_bestdiv(hw, rate, prate);

		return *prate / div;
		return DIV_ROUND_UP(*prate, div);
		}

		static int ti_clk_divider_set_rate(struct clk_hw *hw, unsigned long rate,
		@@ -216,7 +216,7 @@ static int ti_clk_divider_set_rate(struct clk_hw *hw, unsigned long rate,
		unsigned long flags = 0;
		u32 val;

		div = parent_rate / rate;
		div = DIV_ROUND_UP(parent_rate, rate);
		value = _get_val(divider, div);

		if (value > div_mask(divider))

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