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author | Uwe Kleine-König <u.kleine-koenig@pengutronix.de> | 2015-02-21 10:40:25 (GMT) |
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committer | Michael Turquette <mturquette@linaro.org> | 2015-03-09 21:20:17 (GMT) |
commit | 9315514252a95bca37be3ef8a93f835ed91c2855 (patch) | |
tree | a417b7e7a6bb53985e43927518ae2e108ee01f95 /drivers/clk | |
parent | 26bac95aa88c2b1747808c0b885abe7814c0165d (diff) | |
download | linux-9315514252a95bca37be3ef8a93f835ed91c2855.tar.xz |
clk: divider: fix calculation of initial best divider when rounding to closest
Similar to the reasoning for the previous commit
DIV_ROUND_CLOSEST(parent_rate, rate)
might not be the best integer divisor to get a good approximation for
rate from parent_rate (given the metric for CLK_DIVIDER_ROUND_CLOSEST).
For example assume a parent rate of 1000 Hz and a target rate of 700.
Using DIV_ROUND_CLOSEST the suggested divisor gets calculated to 1
resulting in a target rate of 1000 with a delta of 300 to the desired
rate. With choosing 2 as divisor however the resulting rate is 500 which
is nearer to 700.
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>
Diffstat (limited to 'drivers/clk')
-rw-r--r-- | drivers/clk/clk-divider.c | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c index 78b2e65..25006a8 100644 --- a/drivers/clk/clk-divider.c +++ b/drivers/clk/clk-divider.c @@ -219,17 +219,18 @@ static int _div_round_closest(const struct clk_div_table *table, unsigned long parent_rate, unsigned long rate, unsigned long flags) { - int up, down, div; + int up, down; unsigned long up_rate, down_rate; - up = down = div = DIV_ROUND_CLOSEST(parent_rate, rate); + up = DIV_ROUND_UP(parent_rate, rate); + down = parent_rate / rate; if (flags & CLK_DIVIDER_POWER_OF_TWO) { - up = __roundup_pow_of_two(div); - down = __rounddown_pow_of_two(div); + up = __roundup_pow_of_two(up); + down = __rounddown_pow_of_two(down); } else if (table) { - up = _round_up_table(table, div); - down = _round_down_table(table, div); + up = _round_up_table(table, up); + down = _round_down_table(table, down); } up_rate = DIV_ROUND_UP(parent_rate, up); |