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pwm: mxs: Avoid a division in mxs_pwm_apply()

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Since the divisor is not a compile-time constant (unless gcc somehow
decided to unroll the loop PERIOD_CDIV_MAX times), this does a
somewhat expensive 32/32 division. Replace that with a right shift.

We still have a 64/32 division just below, but at least in that
case the divisor is compile-time constant.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
This commit is contained in:
Rasmus Villemoes 2019-10-04 15:32:06 +02:00 committed by Thierry Reding
parent 366486e0af
commit 3c64ed74d6
1 changed files with 3 additions and 3 deletions
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6
drivers/pwm/pwm-mxs.c
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@ -33,8 +33,8 @@
#define PERIOD_CDIV(div) (((div) & 0x7) << 20)
#define PERIOD_CDIV_MAX 8
static const unsigned int cdiv[PERIOD_CDIV_MAX] = {
1, 2, 4, 8, 16, 64, 256, 1024
static const u8 cdiv_shift[PERIOD_CDIV_MAX] = {
0, 1, 2, 3, 4, 6, 8, 10
};
struct mxs_pwm_chip {
@ -71,7 +71,7 @@ static int mxs_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
rate = clk_get_rate(mxs->clk);
while (1) {
c = rate / cdiv[div];
c = rate >> cdiv_shift[div];
c = c * state->period;
do_div(c, 1000000000);
if (c < PERIOD_PERIOD_MAX)