[PATCH v3 2/4] pwm: jz4740: Enhance precision in calculation of duty cycle

[PATCH v3 2/4] pwm: jz4740: Enhance precision in calculation of duty cycle

[Paul Cercueil]

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>
---

Notes:
    v2: New patch. I don't consider this a fix but an enhancement, since the old
    	behaviour was in place since the driver was born in ~2010, so no Fixes tag.
    v3: Add Fixes tag and Uwe's Reviewed-by

 drivers/pwm/pwm-jz4740.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

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)
-- 
2.26.2

Re: [PATCH v3 2/4] pwm: jz4740: Enhance precision in calculation of duty cycle

[Sasha Levin]

Hi

[This is an automated email]

This commit has been processed because it contains a "Fixes:" tag
fixing commit: f6b8a5700057 ("pwm: Add Ingenic JZ4740 support").

The bot has tested the following trees: v5.6.14, v5.4.42, v4.19.124, v4.14.181, v4.9.224, v4.4.224.

v5.6.14: Failed to apply! Possible dependencies:
    485b56f08f33 ("pwm: jz4740: Improve algorithm of clock calculation")
    ce1f9cece057 ("pwm: jz4740: Use clocks from TCU driver")

v5.4.42: Failed to apply! Possible dependencies:
    485b56f08f33 ("pwm: jz4740: Improve algorithm of clock calculation")
    ce1f9cece057 ("pwm: jz4740: Use clocks from TCU driver")

v4.19.124: Failed to apply! Possible dependencies:
    1ac99c58bda9 ("pwm: jz4740: Apply configuration atomically")
    485b56f08f33 ("pwm: jz4740: Improve algorithm of clock calculation")
    ce1f9cece057 ("pwm: jz4740: Use clocks from TCU driver")

v4.14.181: Failed to apply! Possible dependencies:
    174dcc8eaec5 ("pwm: jz4740: Implement ->set_polarity()")
    1ac99c58bda9 ("pwm: jz4740: Apply configuration atomically")
    485b56f08f33 ("pwm: jz4740: Improve algorithm of clock calculation")
    b419006275db ("pwm: jz4740: Enable for all Ingenic SoCs")
    ce1f9cece057 ("pwm: jz4740: Use clocks from TCU driver")

v4.9.224: Failed to apply! Possible dependencies:
    174dcc8eaec5 ("pwm: jz4740: Implement ->set_polarity()")
    1ac99c58bda9 ("pwm: jz4740: Apply configuration atomically")
    485b56f08f33 ("pwm: jz4740: Improve algorithm of clock calculation")
    b419006275db ("pwm: jz4740: Enable for all Ingenic SoCs")
    ce1f9cece057 ("pwm: jz4740: Use clocks from TCU driver")

v4.4.224: Failed to apply! Possible dependencies:
    174dcc8eaec5 ("pwm: jz4740: Implement ->set_polarity()")
    1ac99c58bda9 ("pwm: jz4740: Apply configuration atomically")
    485b56f08f33 ("pwm: jz4740: Improve algorithm of clock calculation")
    b419006275db ("pwm: jz4740: Enable for all Ingenic SoCs")
    ce1f9cece057 ("pwm: jz4740: Use clocks from TCU driver")


NOTE: The patch will not be queued to stable trees until it is upstream.

How should we proceed with this patch?

-- 
Thanks
Sasha