| Message ID | b9208d9b-c7bb-49a3-85d9-231c8b41eb8c@raspberrypi.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
Hi Phil, > Phil Elwell <phil@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 <phil@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? > + > + /* Return a value which is the maximum deviation > + * below the ideal rate, for use as a metric. > + */ Please fix coding style of the comment. Thanks Stefan -- To unsubscribe from this list: send the line "unsubscribe linux-clk" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi Stefan, On 30/05/2017 20:04, Stefan Wahren wrote: > Hi Phil, > >> Phil Elwell <phil@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 <phil@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. Thanks, Phil -- To unsubscribe from this list: send the line "unsubscribe linux-clk" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 <phil@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 <phil@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 -- To unsubscribe from this list: send the line "unsubscribe linux-clk" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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); + + /* Return a value which is the maximum deviation + * below the ideal rate, for use as a metric. + */ + if ((tmp_rate - low) < (high - tmp_rate)) + tmp_rate = low; + else + tmp_rate -= high - tmp_rate; + } + return tmp_rate; } if (data->frac_bits) @@ -1167,6 +1191,7 @@ static unsigned long bcm2835_clock_choose_div_and_prate(struct clk_hw *hw, *div = curdiv << CM_DIV_FRAC_BITS; *prate = curdiv * best_rate; + *avgrate = best_rate; return best_rate; } @@ -1178,6 +1203,7 @@ static int bcm2835_clock_determine_rate(struct clk_hw *hw, bool current_parent_is_pllc; unsigned long rate, best_rate = 0; unsigned long prate, best_prate = 0; + unsigned long avgrate, best_avgrate = 0; size_t i; u32 div; @@ -1202,11 +1228,13 @@ static int bcm2835_clock_determine_rate(struct clk_hw *hw, continue; rate = bcm2835_clock_choose_div_and_prate(hw, i, req->rate, - &div, &prate); + &div, &prate, + &avgrate); if (rate > best_rate && rate <= req->rate) { best_parent = parent; best_prate = prate; best_rate = rate; + best_avgrate = avgrate; } } @@ -1216,7 +1244,7 @@ static int bcm2835_clock_determine_rate(struct clk_hw *hw, req->best_parent_hw = best_parent; req->best_parent_rate = best_prate; - req->rate = best_rate; + req->rate = best_avgrate; return 0; } @@ -2010,6 +2038,7 @@ struct bcm2835_clk_desc { .int_bits = 12, .frac_bits = 12, .is_mash_clock = true, + .low_jitter = true, .parents = bcm2835_pcm_per_parents, .tcnt_mux = 23), [BCM2835_CLOCK_PWM] = REGISTER_PER_CLK(
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 <phil@raspberrypi.org> --- drivers/clk/bcm/clk-bcm2835.c | 39 ++++++++++++++++++++++++++++++++++----- 1 file changed, 34 insertions(+), 5 deletions(-)