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pwm: jz4740: Enhance precision in calculation of duty cycle

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commit 9017dc4fbd59c09463019ce494cfe36d654495a8 upstream.

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: f6b8a57000 ("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>
[ukl: backport to v5.4.y and adapt commit log accordingly]
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Paul Cercueil 2020-05-27 13:52:23 +02:00 • committed by Greg Kroah-Hartman
commit a6030d71e6
1 changed files with 2 additions and 2 deletions
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4
drivers/pwm/pwm-jz4740.c
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@ -108,8 +108,8 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
if (prescaler == 6)
return -EINVAL;
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)