The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 9017dc4fbd59c09463019ce494cfe36d654495a8 Mon Sep 17 00:00:00 2001
From: Paul Cercueil paul@crapouillou.net Date: Wed, 27 May 2020 13:52:23 +0200 Subject: [PATCH] pwm: jz4740: Enhance precision in calculation of duty cycle MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit
Calculating the hardware value for the duty from the hardware value of the period resulted in a precision loss versus calculating it from the clock rate directly.
(Also remove a cast that doesn't really need to be here)
Fixes: f6b8a5700057 ("pwm: Add Ingenic JZ4740 support") Cc: stable@vger.kernel.org Suggested-by: Uwe Kleine-König u.kleine-koenig@pengutronix.de Reviewed-by: Uwe Kleine-König u.kleine-koenig@pengutronix.de Signed-off-by: Paul Cercueil paul@crapouillou.net Signed-off-by: Thierry Reding thierry.reding@gmail.com
diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c index 3cd5c054ad9a..4fe9d99ac9a9 100644 --- a/drivers/pwm/pwm-jz4740.c +++ b/drivers/pwm/pwm-jz4740.c @@ -158,11 +158,11 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, /* Calculate period value */ tmp = (unsigned long long)rate * state->period; do_div(tmp, NSEC_PER_SEC); - period = (unsigned long)tmp; + period = tmp;
/* Calculate duty value */ - tmp = (unsigned long long)period * state->duty_cycle; - do_div(tmp, state->period); + tmp = (unsigned long long)rate * state->duty_cycle; + do_div(tmp, NSEC_PER_SEC); duty = period - tmp;
if (duty >= period)