linux-kernel - Re: [PATCH v3 1/2] pwm-pca9685: Fix several driver bugs

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Message-ID: <20150720093141.GR29614@ulmo>
Date:	Mon, 20 Jul 2015 11:31:41 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Clemens Gruber <clemens.gruber@...ruber.com>
Cc:	linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Steffen Trumtrar <s.trumtrar@...gutronix.de>
Subject: Re: [PATCH v3 1/2] pwm-pca9685: Fix several driver bugs

On Mon, Jul 20, 2015 at 11:27:23AM +0200, Thierry Reding wrote:
> On Mon, Jul 20, 2015 at 10:36:08AM +0200, Clemens Gruber wrote:
> > Problems:
> > - When duty_ns == period_ns, the full OFF bit was not cleared and the
> >   PWM output of the PCA9685 stayed off.
> > - When duty_ns == period_ns and the catch-all channel was used, the
> >   ALL_LED_OFF_L register was not cleared.
> > - The full ON bit was not cleared when setting the OFF time, therefore
> >   the exact OFF time was ignored when setting a duty_ns < period_ns
> > 
> > Solution: Clear both OFF registers when setting full ON and clear the
> > full ON bit when changing the OFF registers.
> > 
> > Cc: Thierry Reding <thierry.reding@...il.com>
> > Cc: Steffen Trumtrar <s.trumtrar@...gutronix.de>
> > Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
> > ---
> >  drivers/pwm/pwm-pca9685.c | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> > 
> > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> > index 34b5c27..f4a9c4a 100644
> > --- a/drivers/pwm/pwm-pca9685.c
> > +++ b/drivers/pwm/pwm-pca9685.c
> > @@ -85,6 +85,22 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> >  	}
> >  
> >  	if (duty_ns == period_ns) {
> > +		/* Clear both OFF registers */
> > +		if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > +			reg = PCA9685_ALL_LED_OFF_L;
> > +		else
> > +			reg = LED_N_OFF_L(pwm->hwpwm);
> > +
> > +		regmap_write(pca->regmap, reg, 0x0);
> > +
> > +		if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > +			reg = PCA9685_ALL_LED_OFF_H;
> > +		else
> > +			reg = LED_N_OFF_H(pwm->hwpwm);
> > +
> > +		regmap_write(pca->regmap, reg, 0x0);
> > +
> > +		/* Set the full ON bit */
> >  		if (pwm->hwpwm >= PCA9685_MAXCHAN)
> >  			reg = PCA9685_ALL_LED_ON_H;
> >  		else
> > @@ -112,6 +128,14 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> >  
> >  	regmap_write(pca->regmap, reg, ((int)duty >> 8) & 0xf);
> >  
> > +	/* Clear the full ON bit, otherwise the set OFF time has no effect */
> > +	if (pwm->hwpwm >= PCA9685_MAXCHAN)
> > +		reg = PCA9685_ALL_LED_ON_H;
> > +	else
> > +		reg = LED_N_ON_H(pwm->hwpwm);
> > +
> > +	regmap_write(pca->regmap, reg, 0);
> 
> Doesn't this undo the setting of this register back up in the duty_ns ==
> period_ns conditional block?

Nevermind, looking at the full driver code I see that the branch returns
0.

Thierry

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