From: Thierry Reding <thierry.reding@gmail.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: linux-pwm@vger.kernel.org,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
Ludovic Desroches <ludovic.desroches@microchip.com>,
kernel@pengutronix.de, Lee Jones <lee.jones@linaro.org>,
Claudiu Beznea <claudiu.beznea@microchip.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/2] pwm: atmel: Improve duty cycle calculation in .apply()
Date: Fri, 23 Apr 2021 19:07:32 +0200 [thread overview]
Message-ID: <YIL+1APYTqWSKRIc@orome.fritz.box> (raw)
In-Reply-To: <20210420095118.1571344-2-u.kleine-koenig@pengutronix.de>
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On Tue, Apr 20, 2021 at 11:51:18AM +0200, Uwe Kleine-König wrote:
> In the calculation of the register value determining the duty cycle the
> requested period is used instead of the actually implemented period which
> results in suboptimal settings.
>
> The following example assumes an input clock of 133333333 Hz on one of
> the SoCs with 16 bit period.
>
> When the following state is to be applied:
>
> .period = 414727681
> .duty_cycle = 652806
>
> the following register values used to be calculated:
>
> PRES = 10
> CPRD = 54000
> CDTY = 53916
>
> which yields an actual duty cycle of a bit more than 645120 ns.
>
> The setting
>
> PRES = 10
> CPRD = 54000
> CDTY = 53915
>
> however yields a duty of 652800 ns which is between the current result
> and the requested value and so is a better approximation.
>
> The reason for this error is that for the calculation of CDTY the
> requested period was used instead of the actually implemented one.
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> ---
> drivers/pwm/pwm-atmel.c | 23 ++++++++++++++++-------
> 1 file changed, 16 insertions(+), 7 deletions(-)
Applied, thanks.
Thierry
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next prev parent reply other threads:[~2021-04-23 17:08 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-20 9:51 [PATCH 1/2] pwm: atmel: Fix duty cycle calculation in .get_state() Uwe Kleine-König
2021-04-20 9:51 ` [PATCH 2/2] pwm: atmel: Improve duty cycle calculation in .apply() Uwe Kleine-König
2021-04-23 17:07 ` Thierry Reding [this message]
2021-04-21 9:26 ` [PATCH] pwm: atmel: rework tracking updates pending in hardware Uwe Kleine-König
[not found] ` <20210421110336.bd5s6e2kjxqilddi@pengutronix.de>
2021-04-21 13:48 ` overflow and wrong timeout errors in pwm-atmel Uwe Kleine-König
2021-04-21 14:18 ` Alexandre Belloni
2021-04-21 15:26 ` Uwe Kleine-König
2021-07-05 7:55 ` [PATCH] pwm: atmel: rework tracking updates pending in hardware Uwe Kleine-König
2021-04-23 17:07 ` [PATCH 1/2] pwm: atmel: Fix duty cycle calculation in .get_state() Thierry Reding
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