Commit 3c64ed74 authored by Rasmus Villemoes's avatar Rasmus Villemoes Committed by Thierry Reding
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pwm: mxs: Avoid a division in mxs_pwm_apply() 



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: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent 366486e0

drivers/pwm/pwm-mxs.c

+3 −3
Original line number Diff line number Diff line
@@ -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)