From: Rasmus Villemoes Date: Fri, 4 Oct 2019 13:32:06 +0000 (+0200) Subject: pwm: mxs: Avoid a division in mxs_pwm_apply() X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=3c64ed74d619c25c65abb1fcafcb1aff835867d5;p=linux.git 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 Reviewed-by: Uwe Kleine-König Signed-off-by: Thierry Reding --- diff --git a/drivers/pwm/pwm-mxs.c b/drivers/pwm/pwm-mxs.c index 57562221c4397..f2e57fcf8f8bc 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)