Hi Stefan, On 30/05/2017 20:04, Stefan Wahren wrote: > Hi Phil, > >> Phil Elwell <[email protected]> hat am 30. Mai 2017 um 18:28 geschrieben: >> >> >> Fractional clock dividers generate accurate average frequencies but >> with jitter, particularly when the integer divisor is small. >> >> Introduce a new metric of clock accuracy to penalise clocks with a good >> average but worse jitter compared to clocks with an average which is no >> better but with lower jitter. The metric is the ideal rate minus the >> worse deviation from that ideal using the nearest integer divisors. >> >> Use this metric for parent selection for clocks requiring low jitter >> (currently just PCM). >> >> Signed-off-by: Phil Elwell <[email protected]> >> --- >> drivers/clk/bcm/clk-bcm2835.c | 39 ++++++++++++++++++++++++++++++++++----- >> 1 file changed, 34 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c >> index facc346..e0ce5e7 100644 >> --- a/drivers/clk/bcm/clk-bcm2835.c >> +++ b/drivers/clk/bcm/clk-bcm2835.c >> @@ -530,6 +530,7 @@ struct bcm2835_clock_data { >> >> bool is_vpu_clock; >> bool is_mash_clock; >> + bool low_jitter; >> >> u32 tcnt_mux; >> }; >> @@ -1124,7 +1125,8 @@ static unsigned long >> bcm2835_clock_choose_div_and_prate(struct clk_hw *hw, >> int parent_idx, >> unsigned long rate, >> u32 *div, >> - unsigned long *prate) >> + unsigned long *prate, >> + unsigned long *avgrate) >> { >> struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw); >> struct bcm2835_cprman *cprman = clock->cprman; >> @@ -1136,11 +1138,33 @@ static unsigned long >> bcm2835_clock_choose_div_and_prate(struct clk_hw *hw, >> parent = clk_hw_get_parent_by_index(hw, parent_idx); >> >> if (!(BIT(parent_idx) & data->set_rate_parent)) { >> + unsigned long tmp_rate; >> + >> *prate = clk_hw_get_rate(parent); >> *div = bcm2835_clock_choose_div(hw, rate, *prate, true); >> >> - return bcm2835_clock_rate_from_divisor(clock, *prate, >> - *div); >> + tmp_rate = bcm2835_clock_rate_from_divisor(clock, *prate, *div); >> + *avgrate = tmp_rate; >> + >> + if (data->low_jitter && (*div & CM_DIV_FRAC_MASK)) { >> + unsigned long high, low; >> + u32 idiv = *div & ~CM_DIV_FRAC_MASK; >> + >> + high = bcm2835_clock_rate_from_divisor(clock, *prate, >> + idiv); >> + idiv += CM_DIV_FRAC_MASK + 1; >> + low = bcm2835_clock_rate_from_divisor(clock, *prate, >> + idiv); > > What about int_div or intdiv instead of idiv as variable name?
OK - int_div matches tmp_rate. >> + >> + /* Return a value which is the maximum deviation >> + * below the ideal rate, for use as a metric. >> + */ > > Please fix coding style of the comment. Oops. I'm surprised checkpatch didn't complain about that. Thanks, Phil
