Commit 3c64ed74 authored Oct 04, 2019 by Rasmus Villemoes Committed by Thierry Reding Jan 08, 2020

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: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry 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)

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