Re: [PATCH 13/14] regulator: pwm: Support extra continuous mode cases

From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Brian Norris <briannorris@chromium.org>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	linux-pwm@vger.kernel.org, Mark Brown <broonie@kernel.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Heiko Stuebner <heiko@sntech.de>,
	linux-rockchip@lists.infradead.org,
	Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Kumar Gala <galak@codeaurora.org>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, Milo Kim <milo.kim@ti.com>,
	Doug Anderson <dianders@google.com>,
	Caesar Wang <wxt@rock-chips.com>,
	Stephen Barber <smbarber@chromium.org>,
	Srinivas Kandagatla <srinivas.kandagatla@gmail.com>,
	Maxime Coquelin <maxime.coquelin@st.com>,
	Patrice Chotard <patrice.chotard@st.com>,
	kernel@stlinux.com
Subject: Re: [PATCH 13/14] regulator: pwm: Support extra continuous mode cases
Date: Sat, 4 Jun 2016 08:30:09 +0200	[thread overview]
Message-ID: <20160604083009.25e7fac6@bbrezillon> (raw)
In-Reply-To: <20160603210308.GK124478@google.com>

On Fri, 3 Jun 2016 14:03:08 -0700
Brian Norris <briannorris@chromium.org> wrote:

> Hi Boris,
> 
> On Fri, Jun 03, 2016 at 10:23:11AM +0200, Boris Brezillon wrote:
> > The continuous mode allows one to declare a PWM regulator without having
> > to declare the voltage <-> dutycycle association table. It works fine as
> > long as your voltage(dutycycle) function is linear, but also has the
> > following constraints:
> > 
> > - dutycycle for min_uV = 0%
> > - dutycycle for max_uV = 100%
> > - dutycycle for min_uV < dutycycle for max_uV
> > 
> > While the linearity constraint is acceptable for now, we sometimes need to
> > restrict of the PWM range (to limit the maximum/minimum voltage for
> > example) or have a min_uV_dutycycle > max_uV_dutycycle (this could be
> > tweaked with PWM polarity, but not all PWMs support inverted polarity).
> > 
> > Add the pwm-dutycycle-range and pwm-dutycycle-unit DT properties to define
> > such constraints. If those properties are not defined, the PWM regulator
> > use the default pwm-dutycycle-range = <0 100> and
> > pwm-dutycycle-unit = <100> values (existing behavior).
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> > ---
> >  drivers/regulator/pwm-regulator.c | 80 ++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 71 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/regulator/pwm-regulator.c b/drivers/regulator/pwm-regulator.c
> > index c39ecd1..2e70eb1 100644
> > --- a/drivers/regulator/pwm-regulator.c
> > +++ b/drivers/regulator/pwm-regulator.c  
> 
> ...
> 
> > @@ -132,31 +141,67 @@ static int pwm_regulator_is_enabled(struct regulator_dev *dev)
> >  static int pwm_regulator_get_voltage(struct regulator_dev *rdev)
> >  {
> >  	struct pwm_regulator_data *drvdata = rdev_get_drvdata(rdev);
> > +	unsigned int min_uV_duty = drvdata->continuous.min_uV_dutycycle;
> > +	unsigned int max_uV_duty = drvdata->continuous.max_uV_dutycycle;
> > +	unsigned int duty_unit = drvdata->continuous.dutycycle_unit;
> >  	int min_uV = rdev->constraints->min_uV;
> > -	int diff = rdev->constraints->max_uV - min_uV;
> > +	int max_uV = rdev->constraints->max_uV;
> > +	int diff_uV = max_uV - min_uV;
> >  	struct pwm_state pstate;
> > +	unsigned int diff_duty;
> > +	unsigned int voltage;
> >  
> >  	pwm_get_state(drvdata->pwm, &pstate);
> >  
> > -	return min_uV + pwm_get_relative_duty_cycle(&pstate, diff);
> > +	voltage = pwm_get_relative_duty_cycle(&pstate, duty_unit);
> > +
> > +	if (max_uV_duty < min_uV_duty) {  
> 
> I still might have appreciated a comment above this line (and similar
> in set_voltage()) to help explain why max can be less than min -- you
> have it in the commit message, but nowhere in the code. Not a big deal,
> and the code looks otherwise good:

Sure, I'll add more comments in the next version.

Thanks,

Boris

> 
> Reviewed-by: Brian Norris <briannorris@chromium.org>
> Tested-by: Brian Norris <briannorris@chromium.org>
> 
> 
> > +		voltage = min_uV_duty - voltage;
> > +		diff_duty = min_uV_duty - max_uV_duty;
> > +	} else {
> > +		voltage = voltage - min_uV_duty;
> > +		diff_duty = max_uV_duty - min_uV_duty;
> > +	}
> > +
> > +	voltage = DIV_ROUND_CLOSEST_ULL((u64)voltage * diff_uV, diff_duty);
> > +
> > +	return voltage + min_uV;
> >  }
> >  
> >  static int pwm_regulator_set_voltage(struct regulator_dev *rdev,
> > -					int min_uV, int max_uV,
> > -					unsigned *selector)
> > +				     int req_min_uV, int req_max_uV,
> > +				     unsigned int *selector)
> >  {
> >  	struct pwm_regulator_data *drvdata = rdev_get_drvdata(rdev);
> > +	unsigned int min_uV_duty = drvdata->continuous.min_uV_dutycycle;
> > +	unsigned int max_uV_duty = drvdata->continuous.max_uV_dutycycle;
> > +	unsigned int duty_unit = drvdata->continuous.dutycycle_unit;
> >  	unsigned int ramp_delay = rdev->constraints->ramp_delay;
> > -	unsigned int req_diff = min_uV - rdev->constraints->min_uV;
> > +	int min_uV = rdev->constraints->min_uV;
> > +	int max_uV = rdev->constraints->max_uV;
> > +	int diff_uV = max_uV - min_uV;
> >  	struct pwm_state pstate;
> > -	unsigned int diff;
> > +	unsigned int diff_duty;
> > +	unsigned int dutycycle;
> >  	int ret;
> >  
> >  	pwm_prepare_new_state(drvdata->pwm, &pstate);
> > -	diff = rdev->constraints->max_uV - rdev->constraints->min_uV;
> >  
> > -	/* We pass diff as the scale to get a uV precision. */
> > -	pwm_set_relative_duty_cycle(&pstate, req_diff, diff);
> > +	if (max_uV_duty < min_uV_duty)
> > +		diff_duty = min_uV_duty - max_uV_duty;
> > +	else
> > +		diff_duty = max_uV_duty - min_uV_duty;
> > +
> > +	dutycycle = DIV_ROUND_CLOSEST_ULL((u64)(req_min_uV - min_uV) *
> > +					  diff_duty,
> > +					  diff_uV);
> > +
> > +	if (max_uV_duty < min_uV_duty)
> > +		dutycycle = min_uV_duty - dutycycle;
> > +	else
> > +		dutycycle = min_uV_duty + dutycycle;
> > +
> > +	pwm_set_relative_duty_cycle(&pstate, dutycycle, duty_unit);
> >  
> >  	ret = pwm_apply_state(drvdata->pwm, &pstate);
> >  	if (ret) {  
> 
> [...]
> 
> Brian

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com