Re: [PATCH] pwm: atmel-pwm: fix calculation of prescale value

[Bo Shen]

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@xxxxxxxxxxxxxxx>
>
> Tested-by: Bo Shen <voice.shen@xxxxxxxxx>
> Acked-by: Bo Shen <voice.shen@xxxxxxxxx>
>
> > ---
> >   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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/