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>
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 @@
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);