From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Clemens Gruber <clemens.gruber@pqgruber.com>
Cc: linux-pwm@vger.kernel.org,
Thierry Reding <thierry.reding@gmail.com>,
Sven Van Asbroeck <TheSven73@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 2/7] pwm: pca9685: Support hardware readout
Date: Mon, 29 Mar 2021 18:54:29 +0200 [thread overview]
Message-ID: <20210329165429.ookfliw4eq6zz2sg@pengutronix.de> (raw)
In-Reply-To: <20210329125707.182732-2-clemens.gruber@pqgruber.com>
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On Mon, Mar 29, 2021 at 02:57:02PM +0200, Clemens Gruber wrote:
> Implements .get_state to read-out the current hardware state.
>
> The hardware readout may return slightly different values than those
> that were set in apply due to the limited range of possible prescale and
> counter register values.
>
> Also note that although the datasheet mentions 200 Hz as default
> frequency when using the internal 25 MHz oscillator, the calculated
> period from the default prescaler register setting of 30 is 5079040ns.
>
> Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
> ---
> drivers/pwm/pwm-pca9685.c | 41 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 41 insertions(+)
>
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 0ed1013737e3..fb026a25fb61 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -333,6 +333,46 @@ static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> return 0;
> }
>
> +static void pca9685_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> + struct pwm_state *state)
> +{
> + struct pca9685 *pca = to_pca(chip);
> + unsigned long long duty;
> + unsigned int val = 0;
> +
> + /* Calculate (chip-wide) period from prescale value */
> + regmap_read(pca->regmap, PCA9685_PRESCALE, &val);
> + state->period = (PCA9685_COUNTER_RANGE * 1000 / PCA9685_OSC_CLOCK_MHZ) *
> + (val + 1);
As we have PCA9685_OSC_CLOCK_MHZ = 25 this is an integer calculation
without loss of precision. It might be worth to point that out in a
comment. (Otherwise doing the division at the end might be more
sensible.)
> + /* The (per-channel) polarity is fixed */
> + state->polarity = PWM_POLARITY_NORMAL;
> +
> + if (pwm->hwpwm >= PCA9685_MAXCHAN) {
> + /*
> + * The "all LEDs" channel does not support HW readout
> + * Return 0 and disabled for backwards compatibility
> + */
> + state->duty_cycle = 0;
> + state->enabled = false;
> + return;
> + }
> +
> + duty = pca9685_pwm_get_duty(pca, pwm->hwpwm);
> +
> + state->enabled = !!duty;
> + if (!state->enabled) {
> + state->duty_cycle = 0;
> + return;
> + } else if (duty == PCA9685_COUNTER_RANGE) {
> + state->duty_cycle = state->period;
> + return;
> + }
> +
> + duty *= state->period;
> + state->duty_cycle = duty / PCA9685_COUNTER_RANGE;
.apply uses ROUND_CLOSEST to calculate duty from state->duty_cycle,
still using / here (instead of ROUND_CLOSEST), but again as
PCA9685_OSC_CLOCK_MHZ is 25 this calculation doesn't suffer from
rounding errors. So if you feed the state returned here into .apply
again, there is (as I want it) no change.
The only annoyance is that if PCA9685_PRESCALE holds a value smaller
than 3, .apply() will fail. Not sure there is any saner way to handle
this.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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next prev parent reply other threads:[~2021-03-29 16:55 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-29 12:57 [PATCH v6 1/7] pwm: pca9685: Switch to atomic API Clemens Gruber
2021-03-29 12:57 ` [PATCH v6 2/7] pwm: pca9685: Support hardware readout Clemens Gruber
2021-03-29 15:51 ` Uwe Kleine-König
2021-03-29 16:33 ` Clemens Gruber
2021-03-29 16:54 ` Uwe Kleine-König [this message]
2021-03-29 17:11 ` Clemens Gruber
2021-03-29 17:41 ` Uwe Kleine-König
2021-03-29 12:57 ` [PATCH v6 3/7] pwm: pca9685: Improve runtime PM behavior Clemens Gruber
2021-03-29 15:55 ` Uwe Kleine-König
2021-03-29 16:31 ` Clemens Gruber
2021-03-29 12:57 ` [PATCH v6 4/7] pwm: pca9685: Support staggered output ON times Clemens Gruber
2021-03-29 17:03 ` Uwe Kleine-König
2021-03-29 17:16 ` Clemens Gruber
2021-03-29 18:02 ` Uwe Kleine-König
2021-03-31 12:26 ` Clemens Gruber
2021-03-31 13:55 ` Clemens Gruber
2021-04-01 20:59 ` Uwe Kleine-König
2021-04-01 21:53 ` Clemens Gruber
2021-03-31 16:21 ` Thierry Reding
2021-04-01 7:50 ` Clemens Gruber
2021-04-01 13:47 ` Thierry Reding
2021-04-01 15:19 ` Clemens Gruber
2021-04-02 19:48 ` Uwe Kleine-König
2021-04-01 20:58 ` Uwe Kleine-König
2021-04-01 21:37 ` Clemens Gruber
2021-04-02 20:23 ` Uwe Kleine-König
2021-03-29 12:57 ` [PATCH v6 5/7] dt-bindings: pwm: pca9685: Add nxp,staggered-outputs property Clemens Gruber
2021-04-02 19:52 ` Uwe Kleine-König
2021-03-29 12:57 ` [PATCH v6 6/7] pwm: pca9685: Restrict period change for prescaler users Clemens Gruber
2021-03-29 17:15 ` Uwe Kleine-König
2021-03-29 17:33 ` Clemens Gruber
2021-03-29 17:49 ` Uwe Kleine-König
2021-03-29 12:57 ` [PATCH v6 7/7] pwm: pca9685: Add error messages for failed regmap calls Clemens Gruber
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