From: Thierry Reding <thierry.reding@gmail.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Lee Jones <lee.jones@linaro.org>,
Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
Florian Fainelli <f.fainelli@gmail.com>,
Ray Jui <rjui@broadcom.com>,
Scott Branden <sbranden@broadcom.com>,
Lino Sanfilippo <LinoSanfilippo@gmx.de>,
Sean Young <sean@mess.org>,
linux-pwm@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com,
linux-rpi-kernel@lists.infradead.org, kernel@pengutronix.de
Subject: Re: [PATCH v3] pwm: bcm2835: Improve period and duty cycle calculation
Date: Mon, 22 Mar 2021 11:48:30 +0100 [thread overview]
Message-ID: <YFh1/nKXYFf2yovm@orome.fritz.box> (raw)
In-Reply-To: <20210114204804.143892-1-u.kleine-koenig@pengutronix.de>
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On Thu, Jan 14, 2021 at 09:48:04PM +0100, Uwe Kleine-König wrote:
> With an input clk rate bigger than 2000000000, scaler would have been
> zero which then would have resulted in a division by zero.
>
> Also the originally implemented algorithm divided by the result of a
> division. This nearly always looses precision. Consider a requested period
> of 1000000 ns. With an input clock frequency of 32786885 Hz the hardware
> was configured with an actual period of 983869.007 ns (PERIOD = 32258)
> while the hardware can provide 1000003.508 ns (PERIOD = 32787).
> And note if the input clock frequency was 32786886 Hz instead, the hardware
> was configured to 1016656.477 ns (PERIOD = 33333) while the optimal
> setting results in 1000003.477 ns (PERIOD = 32787).
>
> This patch implements proper range checking and only divides once for
> the calculation of period (and similar for duty_cycle).
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> ---
> Hello,
>
> changes since v2 (Message-Id:
> 20201222221319.2101107-1-u.kleine-koenig@pengutronix.de):
>
> - Add my calculation to the comment explaining the max_period formula
> as discussed with Lino.
>
> Best regards
> Uwe
>
> drivers/pwm/pwm-bcm2835.c | 35 +++++++++++++++++++++++++++--------
> 1 file changed, 27 insertions(+), 8 deletions(-)
Applied, thanks.
Thierry
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prev parent reply other threads:[~2021-03-22 10:48 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-14 20:48 [PATCH v3] pwm: bcm2835: Improve period and duty cycle calculation Uwe Kleine-König
2021-02-26 11:54 ` Thierry Reding
2021-03-01 10:13 ` Aw: " Lino Sanfilippo
2021-03-06 18:28 ` Lino Sanfilippo
2021-03-22 10:48 ` Thierry Reding [this message]
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