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

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Message-Id: <20210719144951.717684587@linuxfoundation.org>
Date:   Mon, 19 Jul 2021 16:52:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>,
        Thierry Reding <thierry.reding@...il.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.13 204/351] pwm: visconti: Fix and simplify period calculation

From: Uwe Kleine-König <u.kleine-koenig@...gutronix.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@...gutronix.de>
Acked-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>
Signed-off-by: Thierry Reding <thierry.reding@...il.com>
Signed-off-by: Sasha Levin <sashal@...nel.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