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pwm: rcar: Improve calculation of divider 

The rcar_pwm_get_clock_division() has a loop to calculate the divider,
but the value of div should be calculatable without a loop. So, this
patch improves it.

This algorithm is suggested by Uwe Kleine-König and Laurent Pinchart.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
This commit is contained in:
Yoshihiro Shimoda 2019-01-09 17:19:08 +09:00 committed by Thierry Reding
parent 8cc2b97039
commit b4f9a7268d
1 changed files with 7 additions and 9 deletions
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16
drivers/pwm/pwm-rcar.c
View File

@ -8,6 +8,8 @@
#include <linux/clk.h>
#include <linux/err.h>
#include <linux/io.h>
#include <linux/log2.h>
#include <linux/math64.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
@ -68,19 +70,15 @@ static void rcar_pwm_update(struct rcar_pwm_chip *rp, u32 mask, u32 data,
static int rcar_pwm_get_clock_division(struct rcar_pwm_chip *rp, int period_ns)
{
unsigned long clk_rate = clk_get_rate(rp->clk);
unsigned long long max; /* max cycle / nanoseconds */
unsigned int div;
u64 div, tmp;
if (clk_rate == 0)
return -EINVAL;
for (div = 0; div <= RCAR_PWM_MAX_DIVISION; div++) {
max = (unsigned long long)NSEC_PER_SEC * RCAR_PWM_MAX_CYCLE *
(1 << div);
do_div(max, clk_rate);
if (period_ns <= max)
break;
}
div = (u64)NSEC_PER_SEC * RCAR_PWM_MAX_CYCLE;
tmp = (u64)period_ns * clk_rate + div - 1;
tmp = div64_u64(tmp, div);
div = ilog2(tmp - 1) + 1;
return (div <= RCAR_PWM_MAX_DIVISION) ? div : -ERANGE;
}