pwm: visconti: Fix and simplify period calculation

With the original code a request for period = 65536000 ns and period =
32768000 ns yields the same register settings (which results in 32768000
ns) because the value for pwmc0 was miscalculated.

Also simplify using that fls(0) is 0.

Fixes: 721b595744f1 ("pwm: visconti: Add Toshiba Visconti SoC PWM support")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

diff --git a/drivers/pwm/pwm-visconti.c b/drivers/pwm/pwm-visconti.c
index 46d90378636614151f96944ea03b7f91698ae1e2..af4e37d3e3a6705f5711bd5134771b43061ca837 100644 (file)
--- a/drivers/pwm/pwm-visconti.c
+++ b/drivers/pwm/pwm-visconti.c
@@ -82,17 +82,14 @@ static int visconti_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
                return -ERANGE;
 
        /*
-        * PWMC controls a divider that divides the input clk by a
-        * power of two between 1 and 8. As a smaller divider yields
-        * higher precision, pick the smallest possible one.
+        * PWMC controls a divider that divides the input clk by a power of two
+        * between 1 and 8. As a smaller divider yields higher precision, pick
+        * the smallest possible one. As period is at most 0xffff << 3, pwmc0 is
+        * in the intended range [0..3].
         */
-       if (period > 0xffff) {
-               pwmc0 = ilog2(period >> 16);
-               if (WARN_ON(pwmc0 > 3))
-                       return -EINVAL;
-       } else {
-               pwmc0 = 0;
-       }
+       pwmc0 = fls(period >> 16);
+       if (WARN_ON(pwmc0 > 3))
+               return -EINVAL;
 
        period >>= pwmc0;
        duty_cycle >>= pwmc0;