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>

diff --git a/drivers/pwm/pwm-mxs.c b/drivers/pwm/pwm-mxs.c
index 5756222..f2e57fc 100644 (file)
--- 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)