Hello Lokesh,
On Tue, Feb 25, 2020 at 10:31:45AM +0530, Lokesh Vutla wrote:
> Hi Uwe,
>
> On 24/02/20 2:37 PM, Uwe Kleine-König wrote:
> > On Mon, Feb 24, 2020 at 10:51:35AM +0530, Lokesh Vutla wrote:
> >> Implement .apply callback and drop the legacy callbacks(enable, disable,
> >> config, set_polarity).
> >>
> >> Signed-off-by: Lokesh Vutla <lokeshvutla@xxxxxx>
> >> ---
> >> drivers/pwm/pwm-omap-dmtimer.c | 141 +++++++++++++++++++--------------
> >> 1 file changed, 80 insertions(+), 61 deletions(-)
> >>
>
> [..snip..]
>
> >> -static int pwm_omap_dmtimer_set_polarity(struct pwm_chip *chip,
> >> - struct pwm_device *pwm,
> >> - enum pwm_polarity polarity)
> >> +/**
> >> + * pwm_omap_dmtimer_apply() - Changes the state of the pwm omap dm timer.
> >> + * @chip: Pointer to PWM controller
> >> + * @pwm: Pointer to PWM channel
> >> + * @state: New sate to apply
> >> + *
> >> + * Return 0 if successfully changed the state else appropriate error.
> >> + */
> >> +static int pwm_omap_dmtimer_apply(struct pwm_chip *chip,
> >> + struct pwm_device *pwm,
> >> + const struct pwm_state *state)
> >> {
> >> struct pwm_omap_dmtimer_chip *omap = to_pwm_omap_dmtimer_chip(chip);
> >> + int ret = 0;
> >>
> >> - /*
> >> - * PWM core will not call set_polarity while PWM is enabled so it's
> >> - * safe to reconfigure the timer here without stopping it first.
> >> - */
> >> mutex_lock(&omap->mutex);
> >> - omap->pdata->set_pwm(omap->dm_timer,
> >> - polarity == PWM_POLARITY_INVERSED,
> >> - true, OMAP_TIMER_TRIGGER_OVERFLOW_AND_COMPARE);
> >> +
> >> + if (pwm_is_enabled(pwm) && !state->enabled) {
> >
> > In my book calling PWM API functions (designed for PWM consumers) is not
> > so nice. I would prefer you checking the hardware registers or cache the
> > state locally instead of relying on the core here.
>
> .start and .stop apis does read the hardware registers and check the state
> before making any changes. Do you want to drop off the pwm_is_enabled(pwm) check
> here?
The IMHO more natural approach would be to look into the hardware
registers instead of asking the framework.
> > It would be great to have a general description at the top of the driver
> > (like for example drivers/pwm/pwm-sifive.c) that answers things like:
> >
> > - Does calling .stop completes the currently running period (it
> > should)?
>
> Existing driver implementation abruptly stops the cycle. I can make changes such
> that it completes the currently running period.
That would be good for correctness.
> > - Does changing polarity, duty_cycle and period complete the running
> > period?
>
> - Polarity can be changed only when the pwm is not running. Ill add extra guards
> to reflect this behavior.
> - Changing duty_cycle and period does complete the running period and new values
> gets reflected in next cycle.
Is there are race with the hardware? I.e. can it happen that when a new
cycle starts just when you configured the new period but not the
duty_cycle yet a mixed cycle is output?
> > - How does the hardware behave on disable? (i.e. does it output the
> > state the pin is at in that moment? Does it go High-Z?)
>
> Now that I am making changes to complete the current period on disable, the pin
> goes to Low after disabling(completing the cycle).
>
> Ill add all these points as you mentioned in v2.
Great
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
