On Mon, Jul 27, 2020 at 02:04:56PM +0800, Tanwar, Rahul wrote:
>
> Hi Uwe,
>
> On 24/7/2020 12:15 am, Uwe Kleine-König wrote:
> > Hello,
> >
> > On Thu, Jul 23, 2020 at 03:44:18PM +0800, Rahul Tanwar wrote:
> >> +static int lgm_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >> + const struct pwm_state *state)
> >> +{
> >> + struct lgm_pwm_chip *pc = to_lgm_pwm_chip(chip);
> >> + u32 duty_cycle, val;
> >> + int ret;
> >> +
> >> + if (!state->enabled) {
> >> + ret = lgm_pwm_enable(chip, 0);
> >> + return ret;
> >> + }
> >> +
> >> + /*
> >> + * HW only supports NORMAL polarity
> >> + * HW supports fixed period which can not be changed/configured by user
> >> + */
> >> + if (state->polarity != PWM_POLARITY_NORMAL ||
> >> + state->period != pc->period)
> >> + return -EINVAL;
> > At least for state->polarity you have to check before state->enabled, as
> > the expectation on
> >
> > .enabled = false
> > .polarity = PWM_POLARITY_INVERSED
> >
> > is that the output becomes constant high. Also as confirmed at the end
> > of v4, state->period < pc->period was the right check to do.
>
> For below case:
>
> .enabled = false
> .polarity = PWM_POLARITY_INVERSED
>
> Since our HW does not support inversed polarity, the output for above case
> is expected to be constant low. And if we disable PWM before checking for
> polarity, the output becomes constant low. The code just does that. Sorry,
> i could not understand what is wrong with the code. It looks correct to me.
As your hardware can only support normal polarity, the code must have:
if (state->polarity != PWM_POLARITY_NORMAL)
return -EINVAL;
if (!state->enabled) {
ret = lgm_pwm_enable(chip, 0);
return ret;
}
That's what I meant writing: "At least for state->polarity you have to
check before state->enabled".
> Given the fact that we support fixed period, if we allow
> state->period < pc->period case then the duty cycle will be evaluated as
> higher than the requested one because the state->period is lesser than
> the actual fixed period supported by the HW. Can you please elaborate
> on why you think we should allow state->period < pc->period case?
You should not allow it. In v4 you had:
if (state->polarity != PWM_POLARITY_NORMAL ||
state->period < pc->period)
return -EINVAL;
That's the right thing to do (even though I was unsettled at one point
and wrote it was wrong). The check in v5 with state->period !=
pc->period is wrong.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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