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Subject[PATCH v2 5/6] pwm: mxs: avoid a division in mxs_pwm_apply()
Date
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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