Messages in this thread | | | Date | Thu, 25 Sep 2014 09:53:15 +0800 | From | Bo Shen <> | Subject | Re: [PATCH] pwm: atmel-pwm: fix calculation of prescale value |
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Hi,
Correct the PWM maintainer Thierry Reding's e-mail address.
and Add linux-arm-kernel ML.
On 09/25/2014 09:50 AM, Bo Shen wrote: > Hi Nikolaus Voss, > > On 09/23/2014 09:30 PM, Nikolaus Voss wrote: >> The prescale value used for calculating the period was incremented >> afterwards, thus the resulting prescale value is by one too high. >> This resulted in a pwm frequency only half as high as requested. >> >> This patch moves the 64 bit division out of the prescale loop to >> correct the above issue and make the calculation more efficient. > > Thanks for your patch. > >> Signed-off-by: Nikolaus Voss <n.voss@weinmann-emt.de> > > Tested-by: Bo Shen <voice.shen@atmel.com> > Acked-by: Bo Shen <voice.shen@atmel.com> > >> --- >> drivers/pwm/pwm-atmel.c | 24 +++++++++++------------- >> 1 file changed, 11 insertions(+), 13 deletions(-) >> >> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c >> index 6e700a5..ff17b5d 100644 >> --- a/drivers/pwm/pwm-atmel.c >> +++ b/drivers/pwm/pwm-atmel.c >> @@ -102,7 +102,7 @@ static int atmel_pwm_config(struct pwm_chip *chip, >> struct pwm_device *pwm, >> int duty_ns, int period_ns) >> { >> struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip); >> - unsigned long clk_rate, prd, dty; >> + unsigned long prd, dty; >> unsigned long long div; >> unsigned int pres = 0; >> u32 val; >> @@ -113,20 +113,18 @@ static int atmel_pwm_config(struct pwm_chip >> *chip, struct pwm_device *pwm, >> return -EBUSY; >> } >> >> - clk_rate = clk_get_rate(atmel_pwm->clk); >> - div = clk_rate; >> + /* Calculate the period cycles and prescale value */ >> + div = (unsigned long long)clk_get_rate(atmel_pwm->clk) * period_ns; >> + do_div(div, (int)1e9); >> >> - /* Calculate the period cycles */ >> while (div > PWM_MAX_PRD) { >> - div = clk_rate / (1 << pres); >> - div = div * period_ns; >> - /* 1/Hz = 100000000 ns */ >> - do_div(div, 1000000000); >> - >> - if (pres++ > PRD_MAX_PRES) { >> - dev_err(chip->dev, "pres exceeds the maximum value\n"); >> - return -EINVAL; >> - } >> + div >>= 1; >> + ++pres; >> + } >> + >> + if (pres > PRD_MAX_PRES) { >> + dev_err(chip->dev, "pres exceeds the maximum value\n"); >> + return -EINVAL; >> } >> >> /* Calculate the duty cycles */ >> > > Best Regards, > Bo Shen
Best Regards, Bo Shen
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