Commit da321133 authored Feb 21, 2015 by Uwe Kleine-König Committed by Michael Turquette Mar 09, 2015

clk: divider: fix calculation of maximal parent rate for a given divider



The rate provided at the output of a clk-divider is calculated as:

	DIV_ROUND_UP(parent_rate, div)

since commit b11d282d (clk: divider: fix rate calculation for
fractional rates). So to yield a rate not bigger than r parent_rate
must be <= r * div.

The effect of choosing a parent rate that is too big as was done before
this patch results in wrongly ruling out good dividers.

Note that this is not a complete fix as __clk_round_rate might return a
value >= its 2nd parameter. Also for dividers with
CLK_DIVIDER_ROUND_CLOSEST set the calculation is not accurate. But this
fixes the test case by Sascha Hauer that uses a chain of three dividers
under a fixed clock.

Fixes: b11d282d (clk: divider: fix rate calculation for fractional rates)
Suggested-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Michael Turquette <mturquette@linaro.org>

parent 2f7bf4af

drivers/clk/clk-divider.c

+1 −7

Original line number	Diff line number	Diff line
		@@ -144,12 +144,6 @@ static unsigned long clk_divider_recalc_rate(struct clk_hw *hw,
		divider->flags);
		}

		/*
		* The reverse of DIV_ROUND_UP: The maximum number which
		* divided by m is r
		*/
		#define MULT_ROUND_UP(r, m) ((r) * (m) + (m) - 1)

		static bool _is_valid_table_div(const struct clk_div_table *table,
		unsigned int div)
		{
		@@ -313,7 +307,7 @@ static int clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate,
		return i;
		}
		parent_rate = __clk_round_rate(__clk_get_parent(hw->clk),
		MULT_ROUND_UP(rate, i));
		rate * i);
		now = DIV_ROUND_UP(parent_rate, i);
		if (_is_best_div(rate, now, best, flags)) {
		bestdiv = i;