From: Clemens Gruber <clemens.gruber@pqgruber.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: linux-pwm@vger.kernel.org,
Thierry Reding <thierry.reding@gmail.com>,
Sven Van Asbroeck <TheSven73@gmail.com>,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 2/8] pwm: pca9685: Support hardware readout
Date: Wed, 7 Apr 2021 11:53:20 +0200 [thread overview]
Message-ID: <YG2BEGsPU8jWzvPq@workstation.tuxnet> (raw)
In-Reply-To: <20210407090943.vshoxqhaha4j6wq7@pengutronix.de>
On Wed, Apr 07, 2021 at 11:09:43AM +0200, Uwe Kleine-König wrote:
> On Wed, Apr 07, 2021 at 09:33:20AM +0200, Clemens Gruber wrote:
> > On Wed, Apr 07, 2021 at 07:31:35AM +0200, Uwe Kleine-König wrote:
> > > On Tue, Apr 06, 2021 at 06:41:34PM +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>
> > > > ---
> > > > Changes since v6:
> > > > - Added a comment regarding the division (Suggested by Uwe)
> > > > - Rebased
> > > >
> > > > drivers/pwm/pwm-pca9685.c | 46 +++++++++++++++++++++++++++++++++++++++
> > > > 1 file changed, 46 insertions(+)
> > > >
> > > > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> > > > index 5a2ce97e71fd..d4474c5ff96f 100644
> > > > --- a/drivers/pwm/pwm-pca9685.c
> > > > +++ b/drivers/pwm/pwm-pca9685.c
> > > > @@ -333,6 +333,51 @@ 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);
> > > > + /*
> > > > + * PCA9685_OSC_CLOCK_MHZ is 25, i.e. an integer divider of 1000.
> > > > + * The following calculation is therefore only a multiplication
> > > > + * and we are not losing precision.
> > > > + */
> > > > + state->period = (PCA9685_COUNTER_RANGE * 1000 / PCA9685_OSC_CLOCK_MHZ) *
> > > > + (val + 1);
> > > > +
> > > > + /* 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;
> > >
> > > Given that with duty = 0 the chip is still "on" and changing the duty
> > > will first complete the currently running period, I'd model duty=0 as
> > > enabled. This also simplifies the code a bit, to something like:
> > >
> > >
> > > state->enabled = true;
> > > duty = pca9685_pwm_get_duty(pca, pwm->hwpwm);
> > > state->duty_cycle = div_round_up(duty * state->period, PCA9685_COUNTER_RANGE);
> > >
> > > (I'm using round-up here assuming apply uses round-down to get
> > > idempotency. In the current patch set state this is wrong however.)
> >
> > So, in your opinion, every requested PWM of the pca9685 should always be
> > enabled by default (from the PWM core viewpoint) ?
> >
> > And this wouldn't break the following because pwm_get_state does not
> > actually read out the hw state:
> > pwm_get_state -> enabled=true duty=0
> > pwm_apply_state -> enabled =false duty=0
> > pwm_get_state -> enabled=false duty=0
>
> I don't see any breakage here. Either there is none or I failed to grasp
> where you see a problem.
Me neither, I was just thinking out loud.
Clemens
next prev parent reply other threads:[~2021-04-07 9:53 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-06 16:41 [PATCH v7 1/8] pwm: pca9685: Switch to atomic API Clemens Gruber
2021-04-06 16:41 ` [PATCH v7 2/8] pwm: pca9685: Support hardware readout Clemens Gruber
2021-04-07 5:31 ` Uwe Kleine-König
2021-04-07 7:33 ` Clemens Gruber
2021-04-07 9:09 ` Uwe Kleine-König
2021-04-07 9:53 ` Clemens Gruber [this message]
2021-04-06 16:41 ` [PATCH v7 3/8] pwm: pca9685: Improve runtime PM behavior Clemens Gruber
2021-04-09 13:03 ` Thierry Reding
2021-04-09 16:08 ` Clemens Gruber
2021-04-06 16:41 ` [PATCH v7 4/8] dt-bindings: pwm: Support new PWM_STAGGERING_ALLOWED flag Clemens Gruber
2021-04-07 5:33 ` Uwe Kleine-König
2021-04-09 12:27 ` Thierry Reding
2021-04-10 14:01 ` Uwe Kleine-König
2021-04-10 14:02 ` Uwe Kleine-König
2021-04-06 16:41 ` [PATCH v7 5/8] pwm: core: " Clemens Gruber
2021-04-07 5:46 ` Uwe Kleine-König
2021-04-07 20:21 ` Clemens Gruber
2021-04-07 21:34 ` Uwe Kleine-König
2021-04-08 12:50 ` Thierry Reding
2021-04-08 15:51 ` Clemens Gruber
2021-04-08 17:36 ` Uwe Kleine-König
2021-04-08 18:14 ` Clemens Gruber
2021-04-09 11:25 ` Thierry Reding
2021-04-09 16:02 ` Clemens Gruber
2021-04-09 21:35 ` Uwe Kleine-König
2021-04-09 11:10 ` Thierry Reding
2021-04-06 16:41 ` [PATCH v7 6/8] pwm: pca9685: " Clemens Gruber
2021-04-06 16:41 ` [PATCH v7 7/8] pwm: pca9685: Restrict period change for enabled PWMs Clemens Gruber
2021-04-07 6:12 ` Uwe Kleine-König
2021-04-07 20:41 ` Clemens Gruber
2021-04-07 21:38 ` Uwe Kleine-König
2021-04-06 16:41 ` [PATCH v7 8/8] pwm: pca9685: Add error messages for failed regmap calls Clemens Gruber
2021-04-07 6:16 ` Uwe Kleine-König
2021-04-07 20:47 ` Clemens Gruber
2021-04-07 21:41 ` Uwe Kleine-König
2021-04-07 5:24 ` [PATCH v7 1/8] pwm: pca9685: Switch to atomic API Uwe Kleine-König
2021-04-07 7:26 ` Clemens Gruber
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