| Message ID | 20170608122416.1993-4-jbrunet@baylibre.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
On 06/08/2017 02:24 PM, Jerome Brunet wrote: > When using input clocks with high rates, such as clk81 (166MHz), the > fin_ns = NSEC_PER_SEC / fin_freq can introduce a significant error. > > Ex: fin_freq = 166666667, NSEC_PER_SEC = 1000000000 > fin_ns = 5,9999999 > > which is, of course, rounded down to 5. This introduce an error of ~20% > on the period requested from the pwm. > > This patch use ps instead of ns (and 64bits integer) to perform the > calculation. This should give a good enough precision. > > Fixes: 211ed630753d ("pwm: Add support for Meson PWM Controller") > Signed-off-by: Jerome Brunet <jbrunet@baylibre.com> > --- > drivers/pwm/pwm-meson.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c > index b911a944744a..4cdc66f7f718 100644 > --- a/drivers/pwm/pwm-meson.c > +++ b/drivers/pwm/pwm-meson.c > @@ -163,7 +163,8 @@ static int meson_pwm_calc(struct meson_pwm *meson, > unsigned int duty, unsigned int period) > { > unsigned int pre_div, cnt, duty_cnt; > - unsigned long fin_freq = -1, fin_ns; > + unsigned long fin_freq = -1; > + u64 fin_ps; > > if (~(meson->inverter_mask >> id) & 0x1) > duty = period - duty; > @@ -179,13 +180,14 @@ static int meson_pwm_calc(struct meson_pwm *meson, > } > > dev_dbg(meson->chip.dev, "fin_freq: %lu Hz\n", fin_freq); > - fin_ns = NSEC_PER_SEC / fin_freq; > + fin_ps = ((u64)NSEC_PER_SEC * 1000) / fin_freq; > > /* Calc pre_div with the period */ > for (pre_div = 0; pre_div < MISC_CLK_DIV_MASK; pre_div++) { > - cnt = DIV_ROUND_CLOSEST(period, fin_ns * (pre_div + 1)); > - dev_dbg(meson->chip.dev, "fin_ns=%lu pre_div=%u cnt=%u\n", > - fin_ns, pre_div, cnt); > + cnt = DIV_ROUND_CLOSEST_ULL((u64)period * 1000, > + fin_ps * (pre_div + 1)); > + dev_dbg(meson->chip.dev, "fin_ps=%llu pre_div=%u cnt=%u\n", > + fin_ps, pre_div, cnt); > if (cnt <= 0xffff) > break; > } > @@ -208,7 +210,8 @@ static int meson_pwm_calc(struct meson_pwm *meson, > channel->lo = cnt; > } else { > /* Then check is we can have the duty with the same pre_div */ > - duty_cnt = DIV_ROUND_CLOSEST(duty, fin_ns * (pre_div + 1)); > + duty_cnt = DIV_ROUND_CLOSEST_ULL((u64)duty * 1000, > + fin_ps * (pre_div + 1)); > if (duty_cnt > 0xffff) { > dev_err(meson->chip.dev, "unable to get duty cycle\n"); > return -EINVAL; > Great, I missed this !! Acked-by: Neil Armstrong <narmstrong@baylibre.com>
On Thu, Jun 08, 2017 at 02:24:16PM +0200, Jerome Brunet wrote: > When using input clocks with high rates, such as clk81 (166MHz), the > fin_ns = NSEC_PER_SEC / fin_freq can introduce a significant error. > > Ex: fin_freq = 166666667, NSEC_PER_SEC = 1000000000 > fin_ns = 5,9999999 > > which is, of course, rounded down to 5. This introduce an error of ~20% > on the period requested from the pwm. > > This patch use ps instead of ns (and 64bits integer) to perform the > calculation. This should give a good enough precision. > > Fixes: 211ed630753d ("pwm: Add support for Meson PWM Controller") > Signed-off-by: Jerome Brunet <jbrunet@baylibre.com> > --- > drivers/pwm/pwm-meson.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c > index b911a944744a..4cdc66f7f718 100644 > --- a/drivers/pwm/pwm-meson.c > +++ b/drivers/pwm/pwm-meson.c > @@ -163,7 +163,8 @@ static int meson_pwm_calc(struct meson_pwm *meson, > unsigned int duty, unsigned int period) > { > unsigned int pre_div, cnt, duty_cnt; > - unsigned long fin_freq = -1, fin_ns; > + unsigned long fin_freq = -1; > + u64 fin_ps; > > if (~(meson->inverter_mask >> id) & 0x1) > duty = period - duty; > @@ -179,13 +180,14 @@ static int meson_pwm_calc(struct meson_pwm *meson, > } > > dev_dbg(meson->chip.dev, "fin_freq: %lu Hz\n", fin_freq); > - fin_ns = NSEC_PER_SEC / fin_freq; > + fin_ps = ((u64)NSEC_PER_SEC * 1000) / fin_freq; This failed to build, so I had to change this division to a do_div(). Thierry
On Thu, 2017-07-06 at 23:21 +0200, Thierry Reding wrote: > On Thu, Jun 08, 2017 at 02:24:16PM +0200, Jerome Brunet wrote: > > When using input clocks with high rates, such as clk81 (166MHz), the > > fin_ns = NSEC_PER_SEC / fin_freq can introduce a significant error. > > > > Ex: fin_freq = 166666667, NSEC_PER_SEC = 1000000000 > > fin_ns = 5,9999999 > > > > which is, of course, rounded down to 5. This introduce an error of ~20% > > on the period requested from the pwm. > > > > This patch use ps instead of ns (and 64bits integer) to perform the > > calculation. This should give a good enough precision. > > > > Fixes: 211ed630753d ("pwm: Add support for Meson PWM Controller") > > Signed-off-by: Jerome Brunet <jbrunet@baylibre.com> > > --- > > drivers/pwm/pwm-meson.c | 15 +++++++++------ > > 1 file changed, 9 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c > > index b911a944744a..4cdc66f7f718 100644 > > --- a/drivers/pwm/pwm-meson.c > > +++ b/drivers/pwm/pwm-meson.c > > @@ -163,7 +163,8 @@ static int meson_pwm_calc(struct meson_pwm *meson, > > unsigned int duty, unsigned int period) > > { > > unsigned int pre_div, cnt, duty_cnt; > > - unsigned long fin_freq = -1, fin_ns; > > + unsigned long fin_freq = -1; > > + u64 fin_ps; > > > > if (~(meson->inverter_mask >> id) & 0x1) > > duty = period - duty; > > @@ -179,13 +180,14 @@ static int meson_pwm_calc(struct meson_pwm *meson, > > } > > > > dev_dbg(meson->chip.dev, "fin_freq: %lu Hz\n", fin_freq); > > - fin_ns = NSEC_PER_SEC / fin_freq; > > + fin_ps = ((u64)NSEC_PER_SEC * 1000) / fin_freq; > > This failed to build, so I had to change this division to a do_div(). Oh ! Indeed :( I have mostly tested with arm64 which is fine. I thought I had tested arm(32) build as well but I just noticed that MESON_PWM option is disabled in multi_v7_defconfig. Thanks for catching and fixing this Thierry ! > > Thierry
diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c index b911a944744a..4cdc66f7f718 100644 --- a/drivers/pwm/pwm-meson.c +++ b/drivers/pwm/pwm-meson.c @@ -163,7 +163,8 @@ static int meson_pwm_calc(struct meson_pwm *meson, unsigned int duty, unsigned int period) { unsigned int pre_div, cnt, duty_cnt; - unsigned long fin_freq = -1, fin_ns; + unsigned long fin_freq = -1; + u64 fin_ps; if (~(meson->inverter_mask >> id) & 0x1) duty = period - duty; @@ -179,13 +180,14 @@ static int meson_pwm_calc(struct meson_pwm *meson, } dev_dbg(meson->chip.dev, "fin_freq: %lu Hz\n", fin_freq); - fin_ns = NSEC_PER_SEC / fin_freq; + fin_ps = ((u64)NSEC_PER_SEC * 1000) / fin_freq; /* Calc pre_div with the period */ for (pre_div = 0; pre_div < MISC_CLK_DIV_MASK; pre_div++) { - cnt = DIV_ROUND_CLOSEST(period, fin_ns * (pre_div + 1)); - dev_dbg(meson->chip.dev, "fin_ns=%lu pre_div=%u cnt=%u\n", - fin_ns, pre_div, cnt); + cnt = DIV_ROUND_CLOSEST_ULL((u64)period * 1000, + fin_ps * (pre_div + 1)); + dev_dbg(meson->chip.dev, "fin_ps=%llu pre_div=%u cnt=%u\n", + fin_ps, pre_div, cnt); if (cnt <= 0xffff) break; } @@ -208,7 +210,8 @@ static int meson_pwm_calc(struct meson_pwm *meson, channel->lo = cnt; } else { /* Then check is we can have the duty with the same pre_div */ - duty_cnt = DIV_ROUND_CLOSEST(duty, fin_ns * (pre_div + 1)); + duty_cnt = DIV_ROUND_CLOSEST_ULL((u64)duty * 1000, + fin_ps * (pre_div + 1)); if (duty_cnt > 0xffff) { dev_err(meson->chip.dev, "unable to get duty cycle\n"); return -EINVAL;
When using input clocks with high rates, such as clk81 (166MHz), the fin_ns = NSEC_PER_SEC / fin_freq can introduce a significant error. Ex: fin_freq = 166666667, NSEC_PER_SEC = 1000000000 fin_ns = 5,9999999 which is, of course, rounded down to 5. This introduce an error of ~20% on the period requested from the pwm. This patch use ps instead of ns (and 64bits integer) to perform the calculation. This should give a good enough precision. Fixes: 211ed630753d ("pwm: Add support for Meson PWM Controller") Signed-off-by: Jerome Brunet <jbrunet@baylibre.com> --- drivers/pwm/pwm-meson.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)