| Message ID | 1424515225-6929-4-git-send-email-u.kleine-koenig@pengutronix.de |
|---|---|
| State | New |
| Headers | show |
Hi Uwe, On 02/21/2015 11:40 AM, Uwe Kleine-König wrote: > 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> > --- > drivers/clk/clk-divider.c | 13 +++++++------ > 1 file changed, 7 insertions(+), 6 deletions(-) > This is correct. Thanks for fixing this. You can add my: Acked-by: Maxime Coquelin <maxime.coquelin@st.com> Best regards, Maxime
diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c index 66a6211b8834..202a17e9a38b 100644 --- a/drivers/clk/clk-divider.c +++ b/drivers/clk/clk-divider.c @@ -201,17 +201,18 @@ static int _div_round_up(struct clk_divider *divider, static int _div_round_closest(struct clk_divider *divider, unsigned long parent_rate, unsigned long rate) { - 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 (divider->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 (divider->table) { - up = _round_up_table(divider->table, div); - down = _round_down_table(divider->table, div); + up = _round_up_table(divider->table, up); + down = _round_down_table(divider->table, down); } up_rate = DIV_ROUND_UP(parent_rate, up);
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> --- drivers/clk/clk-divider.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)