* [PATCH] pwm: atmel-pwm: fix calculation of prescale value
[not found] ` <542374D3.3080308@atmel.com>
@ 2014-09-25 1:53 ` Bo Shen
0 siblings, 0 replies; only message in thread
From: Bo Shen @ 2014-09-25 1:53 UTC (permalink / raw)
To: linux-arm-kernel
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
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2014-09-25 1:53 UTC | newest]
Thread overview: (only message) (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
[not found] <20140924055138.477E540656@mail.steuer-voss.de>
[not found] ` <542374D3.3080308@atmel.com>
2014-09-25 1:53 ` [PATCH] pwm: atmel-pwm: fix calculation of prescale value Bo Shen
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox