[PATCH v2 5/6] pwm: mxs: avoid a division in mxs_pwm_apply()
From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Date: 2019-10-04 13:33:11
Also in:
linux-devicetree, linux-pwm, lkml
Subsystem:
pwm subsystem, the rest · Maintainers:
Uwe Kleine-König, Linus Torvalds
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> --- drivers/pwm/pwm-mxs.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/pwm/pwm-mxs.c b/drivers/pwm/pwm-mxs.c
index 57562221c439..f2e57fcf8f8b 100644
--- a/drivers/pwm/pwm-mxs.c
+++ b/drivers/pwm/pwm-mxs.c@@ -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)
--
2.20.1
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