linux-kernel - [PATCH v3 3/3] pwm: meson: Use mul_u64_u64_div

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Message-ID: <20240425171253.2752877-4-gnstark@salutedevices.com>
Date: Thu, 25 Apr 2024 20:12:53 +0300
From: George Stark <gnstark@...utedevices.com>
To: <u.kleine-koenig@...gutronix.de>, <neil.armstrong@...aro.org>,
	<khilman@...libre.com>, <jbrunet@...libre.com>,
	<martin.blumenstingl@...glemail.com>, <thierry.reding@...il.com>,
	<hkallweit1@...il.com>
CC: <linux-pwm@...r.kernel.org>, <linux-amlogic@...ts.infradead.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	<kernel@...utedevices.com>, George Stark <gnstark@...utedevices.com>
Subject: [PATCH v3 3/3] pwm: meson: Use mul_u64_u64_div_u64() for frequency calculating

While calculating frequency for the given period u64 numbers are
multiplied before division what can lead to overflow in theory so use
secure mul_u64_u64_div_u64() which handles overflow correctly.

Fixes: 329db102a26d ("pwm: meson: make full use of common clock framework")
Suggested-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Signed-off-by: George Stark <gnstark@...utedevices.com>
---
 drivers/pwm/pwm-meson.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
index 4a652d500dfc..b2f97dfb01bb 100644
--- a/drivers/pwm/pwm-meson.c
+++ b/drivers/pwm/pwm-meson.c
@@ -176,7 +176,7 @@ static int meson_pwm_calc(struct pwm_chip *chip, struct pwm_device *pwm,
 
 	dev_dbg(pwmchip_parent(chip), "fin_freq: %ld Hz\n", fin_freq);
 
-	cnt = div_u64(fin_freq * period, NSEC_PER_SEC);
+	cnt = mul_u64_u64_div_u64(fin_freq, period, NSEC_PER_SEC);
 	if (cnt > 0xffff) {
 		dev_err(pwmchip_parent(chip), "unable to get period cnt\n");
 		return -EINVAL;
@@ -191,7 +191,7 @@ static int meson_pwm_calc(struct pwm_chip *chip, struct pwm_device *pwm,
 		channel->hi = 0;
 		channel->lo = cnt;
 	} else {
-		duty_cnt = div_u64(fin_freq * duty, NSEC_PER_SEC);
+		duty_cnt = mul_u64_u64_div_u64(fin_freq, duty, NSEC_PER_SEC);
 
 		dev_dbg(pwmchip_parent(chip), "duty=%llu duty_cnt=%u\n", duty, duty_cnt);
 
-- 
2.25.1