[PATCH 5.13 204/351] pwm: visconti: Fix and simplify period calculation

Greg Kroah-Hartman
2021-07-19T17:43:00Z

From: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

[ Upstream commit 937efa29e70f7f8424b74631375dcb35d82a4614 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/pwm/pwm-visconti.c | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/pwm/pwm-visconti.c b/drivers/pwm/pwm-visconti.c
index 46d903786366..af4e37d3e3a6 100644
--- 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;
--
2.30.2