Hi Uwe,
On 27/7/2020 3:01 pm, Uwe Kleine-König wrote:
> 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".
Ok, i understand your point now.
>> 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.
>
Does that mean we should allow state->period >= pc->period cases?
If the state->period is greater than HW supported pc->period and
if we allow it then the duty cycle will again be evaluated to be
incorrect/higher than requested duty cycle. Am i missing something
else? Thanks.
Regards,
Rahul
