Am 31.05.2017 um 10:33 schrieb Phil Elwell:
> Hi Stefan,
>
> On 30/05/2017 20:04, Stefan Wahren wrote:
>> Hi Phil,
>>
>>> Phil Elwell <p...@raspberrypi.org> 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 <p...@raspberrypi.org>
>>> ---
>>> 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.
The style above is only used for netdev.
>
> Thanks,
>
> Phil
