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

Boris Brezillon
2016-06-04T06:28:48Z

On Fri, 3 Jun 2016 13:50:28 -0700
Brian Norris <briannorris@chromium.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@free-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@chromium.org>
> Tested-by: Brian Norris <briannorris@chromium.org>

--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering