linux-kernel - Re: [PATCH 10/14] regulator: pwm: Switch to the atomic PWM API

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Message-ID: <20160604082848.0b897b14@bbrezillon>
Date:	Sat, 4 Jun 2016 08:28:48 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Brian Norris <briannorris@...omium.org>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	linux-pwm@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	linux-rockchip@...ts.infradead.org,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Milo Kim <milo.kim@...com>,
	Doug Anderson <dianders@...gle.com>,
	Caesar Wang <wxt@...k-chips.com>,
	Stephen Barber <smbarber@...omium.org>,
	Srinivas Kandagatla <srinivas.kandagatla@...il.com>,
	Maxime Coquelin <maxime.coquelin@...com>,
	Patrice Chotard <patrice.chotard@...com>, kernel@...inux.com,
	Laxman Dewangan <ldewangan@...dia.com>
Subject: Re: [PATCH 10/14] regulator: pwm: Switch to the atomic PWM API

On Fri, 3 Jun 2016 13:50:28 -0700
Brian Norris <briannorris@...omium.org> wrote:

> + Laxman
> 
> Hi,
> 
> On Fri, Jun 03, 2016 at 10:23:08AM +0200, Boris Brezillon wrote:
> > Use the atomic API wherever appropriate and get rid of pwm_apply_args()
> > call (the reference period and polarity are now explicitly set when
> > calling pwm_apply_state()).
> > 
> > We also make use of the pwm_set_relative_duty_cycle() helper to ease
> > relative to absolute duty_cycle conversion.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> > ---
> >  drivers/regulator/pwm-regulator.c | 38 ++++++++++----------------------------
> >  1 file changed, 10 insertions(+), 28 deletions(-)
> > 
> > diff --git a/drivers/regulator/pwm-regulator.c b/drivers/regulator/pwm-regulator.c
> > index 524b43f..bf033fd 100644
> > --- a/drivers/regulator/pwm-regulator.c
> > +++ b/drivers/regulator/pwm-regulator.c
> > @@ -59,16 +59,14 @@ static int pwm_regulator_set_voltage_sel(struct regulator_dev *rdev,
> >  					 unsigned selector)
> >  {
> >  	struct pwm_regulator_data *drvdata = rdev_get_drvdata(rdev);
> > -	struct pwm_args pargs;
> > -	int dutycycle;
> > +	struct pwm_state pstate;
> >  	int ret;
> >  
> > -	pwm_get_args(drvdata->pwm, &pargs);
> > +	pwm_prepare_new_state(drvdata->pwm, &pstate);
> > +	pwm_set_relative_duty_cycle(&pstate,
> > +			drvdata->duty_cycle_table[selector].dutycycle, 100);
> >  
> > -	dutycycle = (pargs.period *
> > -		    drvdata->duty_cycle_table[selector].dutycycle) / 100;
> > -
> > -	ret = pwm_config(drvdata->pwm, dutycycle, pargs.period);
> > +	ret = pwm_apply_state(drvdata->pwm, &pstate);
> >  	if (ret) {
> >  		dev_err(&rdev->dev, "Failed to configure PWM: %d\n", ret);
> >  		return ret;
> > @@ -126,34 +124,18 @@ static int pwm_regulator_set_voltage(struct regulator_dev *rdev,
> >  {
> >  	struct pwm_regulator_data *drvdata = rdev_get_drvdata(rdev);
> >  	unsigned int ramp_delay = rdev->constraints->ramp_delay;
> > -	struct pwm_args pargs;
> >  	unsigned int req_diff = min_uV - rdev->constraints->min_uV;
> > +	struct pwm_state pstate;
> >  	unsigned int diff;
> > -	unsigned int duty_pulse;
> > -	u64 req_period;
> > -	u32 rem;
> >  	int ret;
> >  
> > -	pwm_get_args(drvdata->pwm, &pargs);
> > +	pwm_prepare_new_state(drvdata->pwm, &pstate);
> >  	diff = rdev->constraints->max_uV - rdev->constraints->min_uV;
> >  
> > -	/* First try to find out if we get the iduty cycle time which is
> > -	 * factor of PWM period time. If (request_diff_to_min * pwm_period)
> > -	 * is perfect divided by voltage_range_diff then it is possible to
> > -	 * get duty cycle time which is factor of PWM period. This will help
> > -	 * to get output voltage nearer to requested value as there is no
> > -	 * calculation loss.
> > -	 */
> > -	req_period = req_diff * pargs.period;
> > -	div_u64_rem(req_period, diff, &rem);
> > -	if (!rem) {
> > -		do_div(req_period, diff);
> > -		duty_pulse = (unsigned int)req_period;
> > -	} else {
> > -		duty_pulse = (pargs.period / 100) * ((req_diff * 100) / diff);
> > -	}
> > +	/* We pass diff as the scale to get a uV precision. */
> > +	pwm_set_relative_duty_cycle(&pstate, req_diff, diff);  
> 
> Notably, you're dropping much of Laxman's commit fd786fb0276a ("regulator:
> pwm: Try to avoid voltage error in duty cycle calculation"), but I
> believe the DIV_ROUND_CLOSEST_ULL() in pwm_set_relative_duty_cycle()
> solves his problem better.

Oops, forgot to comment on that in the commit message. Indeed, the use
of pwm_set_relative_duty_cycle() solves the problem Laxman was seeing.

> 
> >  
> > -	ret = pwm_config(drvdata->pwm, duty_pulse, pargs.period);
> > +	ret = pwm_apply_state(drvdata->pwm, &pstate);
> >  	if (ret) {
> >  		dev_err(&rdev->dev, "Failed to configure PWM: %d\n", ret);
> >  		return ret;  
> 
> Reviewed-by: Brian Norris <briannorris@...omium.org>
> Tested-by: Brian Norris <briannorris@...omium.org>



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