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 [thread overview]
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/ |
next prev parent reply other threads:[~2019-01-05 19:57 UTC|newest]
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
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