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authorNikolaus Voss <n.voss@weinmann-emt.de>2014-09-23 15:30:21 +0200
committerThierry Reding <thierry.reding@gmail.com>2014-09-25 08:52:39 +0200
commite2e08970100db03bb84fd4a72f9c35bfc18d595a (patch)
tree826f2e39834f3b497da11547a50b37f7fdc6746a /drivers/pwm
parent70145f87139fbc43b726f873813cd91dce371899 (diff)
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pwm: atmel: Fix calculation of prescale value
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.voss@weinmann-emt.de> Tested-by: Bo Shen <voice.shen@atmel.com> Acked-by: Bo Shen <voice.shen@atmel.com> Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm')
-rw-r--r--drivers/pwm/pwm-atmel.c24
1 files changed, 11 insertions, 13 deletions
diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
index 6e700a541ca3..d3c22de9ee47 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, 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++;
+ }
+
+ if (pres > PRD_MAX_PRES) {
+ dev_err(chip->dev, "pres exceeds the maximum value\n");
+ return -EINVAL;
}
/* Calculate the duty cycles */