On Tue, Sep 23, 2014 at 03:30:21PM +0200, 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. > > Signed-off-by: Nikolaus Voss <n.v...@weinmann-emt.de> > --- > drivers/pwm/pwm-atmel.c | 24 +++++++++++------------- > 1 file changed, 11 insertions(+), 13 deletions(-)
Hi Nikolaus,
Please Cc the linux-...@vger.kernel.org mailing list for PWM-related
patches in the future.
Also a couple more comments:
In the patch description: "pwm frequency" should be "PWM frequency".
> 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);
1e9 should be NSEC_PER_SEC.
> - /* 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;
Unless you really need the prefix increment behaviour (you don't in this
case) I prefer using the postfix operator because it is slightly more
idiomatic.
No need for you to respin the patch, I've fixed up the above when
applying.
Thierry
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