Linux-MIPS Archive on lore.kernel.org
 help / color / Atom feed
From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Paul Cercueil <paul@crapouillou.net>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ralf Baechle <ralf@linux-mips.org>,
	Paul Burton <paul.burton@mips.com>,
	James Hogan <jhogan@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	linux-pwm@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-watchdog@vger.kernel.org,
	linux-mips@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-clk@vger.kernel.org
Subject: Re: [PATCH v9 14/27] pwm: jz4740: Improve algorithm of clock calculation
Date: Sat, 5 Jan 2019 20:57:25 +0100
Message-ID: <20190105195725.cuxfge6zkpbt3cyk@pengutronix.de> (raw)
In-Reply-To: <20181227181319.31095-15-paul@crapouillou.net>

On Thu, Dec 27, 2018 at 07:13:06PM +0100, Paul Cercueil wrote:
> The previous algorithm hardcoded details about how the TCU clocks work.
> The new algorithm will use clk_round_rate to find the perfect clock rate
> for the PWM channel.
> 
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> ---
> 
> Notes:
>      v9: New patch
> 
>  drivers/pwm/pwm-jz4740.c | 26 +++++++++++++++-----------
>  1 file changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c
> index c6136bd4434b..dd80a2cf6528 100644
> --- a/drivers/pwm/pwm-jz4740.c
> +++ b/drivers/pwm/pwm-jz4740.c
> @@ -110,23 +110,27 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  	struct jz4740_pwm_chip *jz4740 = to_jz4740(pwm->chip);
>  	struct clk *clk = jz4740->clks[pwm->hwpwm],
>  		   *parent_clk = clk_get_parent(clk);
> -	unsigned long rate, period, duty;
> +	unsigned long rate, new_rate, period, duty;
>  	unsigned long long tmp;
> -	unsigned int prescaler = 0;
>  
>  	rate = clk_get_rate(parent_clk);
> -	tmp = (unsigned long long)rate * state->period;
> -	do_div(tmp, 1000000000);
> -	period = tmp;
>  
> -	while (period > 0xffff && prescaler < 6) {
> -		period >>= 2;
> -		rate >>= 2;
> -		++prescaler;
> +	for (;;) {
> +		tmp = (unsigned long long)rate * state->period;
> +		do_div(tmp, 1000000000);

NSEC_PER_SEC?

> +
> +		if (tmp <= 0xffff)
> +			break;
> +
> +		new_rate = clk_round_rate(clk, rate - 1);
> +
> +		if (new_rate < rate)
> +			rate = new_rate;
> +		else
> +			return -EINVAL;

You are assuming stuff here about the parent clk which isn't guaranteed
(AFAICT) by the clk framework: If you call clk_round_rate(clk, rate - 1)
this might well return rate even if the clock could run slower than
rate.

Wouldn't it make sense to start iterating with rate = 0xffff * 1e9 /
period? Otherwise you get bad configurations if rate is considerable
slower than necessary.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

  reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-27 18:12 [PATCH v9 00/27] Ingenic TCU patchset v9 Paul Cercueil
2018-12-27 18:12 ` [PATCH v9 01/27] dt-bindings: ingenic: Add DT bindings for TCU clocks Paul Cercueil
2018-12-27 18:12 ` [PATCH v9 02/27] doc: Add doc for the Ingenic TCU hardware Paul Cercueil
2018-12-27 18:12 ` [PATCH v9 03/27] dt-bindings: Add doc for the Ingenic TCU drivers Paul Cercueil
2018-12-28 21:48   ` Rob Herring
2018-12-27 18:12 ` [PATCH v9 04/27] clocksource: Add a new timer-ingenic driver Paul Cercueil
2019-02-25 15:55   ` Daniel Lezcano
2019-02-25 22:59     ` Paul Cercueil
2018-12-27 18:12 ` [PATCH v9 05/27] clocksource: Add driver for the Ingenic JZ47xx OST Paul Cercueil
2018-12-27 18:12 ` [PATCH v9 06/27] MAINTAINERS: Add myself as maintainer for Ingenic TCU drivers Paul Cercueil
2018-12-27 18:12 ` [PATCH v9 07/27] watchdog: jz4740: Use WDT clock provided by TCU driver Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 08/27] watchdog: jz4740: Use regmap " Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 09/27] watchdog: jz4740: Avoid starting watchdog in set_timeout Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 10/27] watchdog: jz4740: Drop dependency on MACH_JZ47xx, use COMPILE_TEST Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 11/27] pwm: jz4740: Apply configuration atomically Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 12/27] pwm: jz4740: Use regmap from TCU driver Paul Cercueil
2019-01-05 19:42   ` Uwe Kleine-König
2019-01-05 20:46     ` Paul Cercueil
2019-01-05 21:18       ` Uwe Kleine-König
2018-12-27 18:13 ` [PATCH v9 13/27] pwm: jz4740: Use clocks " Paul Cercueil
2019-01-05 19:45   ` Uwe Kleine-König
2019-01-05 20:52     ` Paul Cercueil
2019-01-05 21:19       ` Uwe Kleine-König
2018-12-27 18:13 ` [PATCH v9 14/27] pwm: jz4740: Improve algorithm of clock calculation Paul Cercueil
2019-01-05 19:57   ` Uwe Kleine-König [this message]
2019-01-05 21:05     ` Paul Cercueil
2019-01-05 21:27       ` Uwe Kleine-König
2019-01-10 14:04         ` Paul Cercueil
2019-02-23  1:17           ` Paul Cercueil
2019-02-28 18:42             ` Stephen Boyd
2018-12-27 18:13 ` [PATCH v9 15/27] pwm: jz4740: Allow selection of PWM channels 0 and 1 Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 16/27] pwm: jz4740: Drop dependency on MACH_INGENIC, use COMPILE_TEST Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 17/27] pwm: jz4740: Remove unused devicetree compatible strings Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 18/27] clk: jz4740: Add TCU clock Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 19/27] MIPS: Kconfig: Select TCU timer driver when MACH_INGENIC is set Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 20/27] MIPS: jz4740: Add DTS nodes for the TCU drivers Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 21/27] MIPS: qi_lb60: Move PWM devices to devicetree Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 22/27] MIPS: qi_lb60: Reduce system timer and clocksource to 750 kHz Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 23/27] MIPS: CI20: Reduce system timer to 3 MHz Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 24/27] MIPS: CI20: defconfig: enable OST driver Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 25/27] MIPS: GCW0: Reduce system timer to 750 kHz Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 26/27] MIPS: GCW0: defconfig: Enable OST, watchdog, PWM drivers Paul Cercueil
2018-12-27 18:13 ` [PATCH v9 27/27] MIPS: jz4740: Drop obsolete code Paul Cercueil

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190105195725.cuxfge6zkpbt3cyk@pengutronix.de \
    --to=u.kleine-koenig@pengutronix.de \
    --cc=corbet@lwn.net \
    --cc=daniel.lezcano@linaro.org \
    --cc=devicetree@vger.kernel.org \
    --cc=jhogan@kernel.org \
    --cc=linux-clk@vger.kernel.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mips@vger.kernel.org \
    --cc=linux-pwm@vger.kernel.org \
    --cc=linux-watchdog@vger.kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=paul.burton@mips.com \
    --cc=paul@crapouillou.net \
    --cc=ralf@linux-mips.org \
    --cc=robh+dt@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=thierry.reding@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-MIPS Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mips/0 linux-mips/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mips linux-mips/ https://lore.kernel.org/linux-mips \
		linux-mips@vger.kernel.org linux-mips@archiver.kernel.org
	public-inbox-index linux-mips


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-mips


AGPL code for this site: git clone https://public-inbox.org/ public-inbox