From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Paul Cercueil <paul@crapouillou.net>
Cc: Thierry Reding <thierry.reding@gmail.com>,
od@zcrc.me, linux-pwm@vger.kernel.org,
linux-kernel@vger.kernel.org,
Mathieu Malaterre <malat@debian.org>,
Artur Rojek <contact@artur-rojek.eu>
Subject: Re: [PATCH 4/7] pwm: jz4740: Improve algorithm of clock calculation
Date: Fri, 9 Aug 2019 19:05:51 +0200 [thread overview]
Message-ID: <20190809170551.u4ybilf5ay2rsvnn@pengutronix.de> (raw)
In-Reply-To: <20190809123031.24219-5-paul@crapouillou.net>
On Fri, Aug 09, 2019 at 02:30:28PM +0200, 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>
> Tested-by: Mathieu Malaterre <malat@debian.org>
> Tested-by: Artur Rojek <contact@artur-rojek.eu>
> ---
> drivers/pwm/pwm-jz4740.c | 60 +++++++++++++++++++++++++++++-----------
> 1 file changed, 44 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c
> index 6ec8794d3b99..f20dc2e19240 100644
> --- a/drivers/pwm/pwm-jz4740.c
> +++ b/drivers/pwm/pwm-jz4740.c
> @@ -110,24 +110,56 @@ 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 = pwm_get_chip_data(pwm),
> *parent_clk = clk_get_parent(clk);
> - unsigned long rate, period, duty;
> + unsigned long rate, parent_rate, period, duty;
> unsigned long long tmp;
> - unsigned int prescaler = 0;
> + int ret;
>
> - rate = clk_get_rate(parent_clk);
> - tmp = (unsigned long long)rate * state->period;
> - do_div(tmp, 1000000000);
> - period = tmp;
> + parent_rate = clk_get_rate(parent_clk);
> +
> + jz4740_pwm_disable(chip, pwm);
>
> - while (period > 0xffff && prescaler < 6) {
> - period >>= 2;
> - rate >>= 2;
> - ++prescaler;
> + /* Reset the clock to the maximum rate, and we'll reduce it if needed */
> + ret = clk_set_max_rate(clk, parent_rate);
What is the purpose of this call? IIUC this limits the allowed range of
rates for clk. I assume the idea is to prevent other consumers to change
the rate in a way that makes it unsuitable for this pwm. But this only
makes sense if you had a notifier for clk changes, doesn't it? I'm
confused.
I think this doesn't match the commit log, you didn't even introduced a
call to clk_round_rate().
> + if (ret) {
> + dev_err(chip->dev, "Unable to set max rate: %d\n", ret);
> + return ret;
> }
>
> - if (prescaler == 6)
> - return -EINVAL;
> + ret = clk_set_rate(clk, parent_rate);
> + if (ret) {
> + dev_err(chip->dev, "Unable to reset to parent rate (%lu Hz)",
> + parent_rate);
> + return ret;
> + }
> +
> + /*
> + * Limit the clock to a maximum rate that still gives us a period value
> + * which fits in 16 bits.
> + */
> + tmp = 0xffffull * NSEC_PER_SEC;
> + do_div(tmp, state->period);
>
> + ret = clk_set_max_rate(clk, tmp);
And now you change the maximal rate again?
> + if (ret) {
> + dev_err(chip->dev, "Unable to set max rate: %d\n", ret);
> + return ret;
> + }
> +
> + /*
> + * Read back the clock rate, as it may have been modified by
> + * clk_set_max_rate()
> + */
> + rate = clk_get_rate(clk);
> +
> + if (rate != parent_rate)
> + dev_dbg(chip->dev, "PWM clock updated to %lu Hz\n", rate);
> +
> + /* Calculate period value */
> + tmp = (unsigned long long)rate * state->period;
> + do_div(tmp, NSEC_PER_SEC);
> + period = (unsigned long)tmp;
> +
> + /* Calculate duty value */
> tmp = (unsigned long long)period * state->duty_cycle;
> do_div(tmp, state->period);
> duty = period - tmp;
> @@ -135,14 +167,10 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> if (duty >= period)
> duty = period - 1;
>
> - jz4740_pwm_disable(chip, pwm);
> -
> /* Set abrupt shutdown */
> regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),
> TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD);
>
> - clk_set_rate(clk, rate);
> -
It's not obvious to me why removing these two lines belong in the
current patch.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
next prev parent reply other threads:[~2019-08-09 17:05 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-09 12:30 [PATCH 0/7] pwm: jz4740: Driver update Paul Cercueil
2019-08-09 12:30 ` [PATCH 1/7] pwm: jz4740: Obtain regmap from parent node Paul Cercueil
2019-08-09 16:51 ` Uwe Kleine-König
2019-08-09 17:04 ` Paul Cercueil
2019-08-12 6:18 ` Uwe Kleine-König
2019-08-09 12:30 ` [PATCH 2/7] pwm: jz4740: Use clocks from TCU driver Paul Cercueil
2019-08-09 16:55 ` Uwe Kleine-König
2019-08-09 12:30 ` [PATCH 3/7] pwm: jz4740: Drop dependency on MACH_INGENIC Paul Cercueil
2019-08-09 16:41 ` Uwe Kleine-König
2019-08-09 21:40 ` Paul Cercueil
2019-08-12 6:09 ` Uwe Kleine-König
2019-08-09 12:30 ` [PATCH 4/7] pwm: jz4740: Improve algorithm of clock calculation Paul Cercueil
2019-08-09 17:05 ` Uwe Kleine-König [this message]
2019-08-09 17:14 ` Paul Cercueil
2019-08-12 6:15 ` Uwe Kleine-König
2019-08-12 20:43 ` Paul Cercueil
2019-08-12 21:48 ` Uwe Kleine-König
2019-08-12 22:25 ` Paul Cercueil
[not found] ` <1565648183.2007.3@crapouillou.net>
2019-08-13 5:27 ` Uwe Kleine-König
2019-08-13 11:01 ` Paul Cercueil
2019-08-13 12:33 ` Uwe Kleine-König
2019-08-13 12:47 ` Paul Cercueil
2019-08-13 14:09 ` Uwe Kleine-König
2019-08-14 16:10 ` Paul Cercueil
2019-08-14 17:32 ` Uwe Kleine-König
2019-10-21 12:47 ` Paul Cercueil
2020-02-12 7:29 ` About rounding in the clk framework [Was: Re: [PATCH 4/7] pwm: jz4740: Improve algorithm of clock calculation] Uwe Kleine-König
2020-04-14 9:24 ` Uwe Kleine-König
2020-12-21 13:57 ` Uwe Kleine-König
2019-08-09 12:30 ` [PATCH 5/7] pwm: jz4740: Allow selection of PWM channels 0 and 1 Paul Cercueil
2019-08-09 12:30 ` [PATCH 6/7] pwm: jz4740: Make PWM start with the active part Paul Cercueil
2019-08-09 17:10 ` Uwe Kleine-König
2019-08-09 17:33 ` Paul Cercueil
2019-08-12 5:55 ` Uwe Kleine-König
2019-08-12 20:50 ` Paul Cercueil
2019-08-12 21:58 ` Uwe Kleine-König
2019-09-20 22:52 ` Thierry Reding
2019-08-09 12:30 ` [PATCH 7/7] pwm: jz4740: document known limitations Paul Cercueil
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