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clk: divider: fix selection of divider when rounding to closest

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It's an invalid approach to assume that among two divider values
the one nearer the exact divider is the better one.

Assume a parent rate of 1000 Hz, a divider with CLK_DIVIDER_POWER_OF_TWO
and a target rate of 89 Hz. The exact divider is ~ 11.236 so 8 and 16
are the candidates to choose from yielding rates 125 Hz and 62.5 Hz
respectivly. While 8 is nearer to 11.236 than 16 is, the latter is still
the better divider as 62.5 is nearer to 89 than 125 is.

Fixes: 774b514390 (clk: divider: Add round to closest divider)
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Michael Turquette <mturquette@linaro.org>
This commit is contained in:
Uwe Kleine-König 2015-02-21 11:40:24 +01:00 committed by Michael Turquette
parent da321133b5
commit 26bac95aa8
1 changed files with 5 additions and 1 deletions
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6
drivers/clk/clk-divider.c
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@ -220,6 +220,7 @@ static int _div_round_closest(const struct clk_div_table *table,
unsigned long flags) unsigned long flags)
{ {
int up, down, div; int up, down, div;
unsigned long up_rate, down_rate;
up = down = div = DIV_ROUND_CLOSEST(parent_rate, rate); up = down = div = DIV_ROUND_CLOSEST(parent_rate, rate);
@ -231,7 +232,10 @@ static int _div_round_closest(const struct clk_div_table *table,
down = _round_down_table(table, div); down = _round_down_table(table, div);
} }
return (up - div) <= (div - down) ? up : down; up_rate = DIV_ROUND_UP(parent_rate, up);
down_rate = DIV_ROUND_UP(parent_rate, down);
return (rate - up_rate) <= (down_rate - rate) ? up : down;
} }
static int _div_round(const struct clk_div_table *table, static int _div_round(const struct clk_div_table *table,