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pwm: atmel: Replace loop in prescale calculation by ad-hoc calculation

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The calculated values are the same with the modified algorithm. The only
difference is that the calculation is a bit more efficient.

Acked-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
This commit is contained in:
Uwe Kleine-König 2019-08-24 02:10:38 +02:00 • committed by Thierry Reding
parent ff55e7a314
commit 2101c878f7
1 changed files with 17 additions and 7 deletions
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24
drivers/pwm/pwm-atmel.c
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@ -60,7 +60,7 @@ struct atmel_pwm_registers {
}; };
struct atmel_pwm_config { struct atmel_pwm_config {
u32 max_period; u32 period_bits;
}; };
struct atmel_pwm_data { struct atmel_pwm_data {
@ -119,17 +119,27 @@ static int atmel_pwm_calculate_cprd_and_pres(struct pwm_chip *chip,
{ {
struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip); struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
unsigned long long cycles = state->period; unsigned long long cycles = state->period;
int shift;
/* Calculate the period cycles and prescale value */ /* Calculate the period cycles and prescale value */
cycles *= clk_get_rate(atmel_pwm->clk); cycles *= clk_get_rate(atmel_pwm->clk);
do_div(cycles, NSEC_PER_SEC); do_div(cycles, NSEC_PER_SEC);
for (*pres = 0; cycles > atmel_pwm->data->cfg.max_period; cycles >>= 1) /*
(*pres)++; * The register for the period length is cfg.period_bits bits wide.
* So for each bit the number of clock cycles is wider divide the input
* clock frequency by two using pres and shift cprd accordingly.
*/
shift = fls(cycles) - atmel_pwm->data->cfg.period_bits;
if (*pres > PWM_MAX_PRES) { if (shift > PWM_MAX_PRES) {
dev_err(chip->dev, "pres exceeds the maximum value\n"); dev_err(chip->dev, "pres exceeds the maximum value\n");
return -EINVAL; return -EINVAL;
} else if (shift > 0) {
*pres = shift;
cycles >>= *pres;
} else {
*pres = 0;
} }
*cprd = cycles; *cprd = cycles;
@ -289,7 +299,7 @@ static const struct atmel_pwm_data atmel_sam9rl_pwm_data = {
}, },
.cfg = { .cfg = {
/* 16 bits to keep period and duty. */ /* 16 bits to keep period and duty. */
.max_period = 0xffff, .period_bits = 16,
}, },
}; };
@ -302,7 +312,7 @@ static const struct atmel_pwm_data atmel_sama5_pwm_data = {
}, },
.cfg = { .cfg = {
/* 16 bits to keep period and duty. */ /* 16 bits to keep period and duty. */
.max_period = 0xffff, .period_bits = 16,
}, },
}; };
@ -315,7 +325,7 @@ static const struct atmel_pwm_data mchp_sam9x60_pwm_data = {
}, },
.cfg = { .cfg = {
/* 32 bits to keep period and duty. */ /* 32 bits to keep period and duty. */
.max_period = 0xffffffff, .period_bits = 32,
}, },
}; };