Re: [PATCH v3 04/15] pwm: lpss: Add range limit check for the base_unit register value

Hans de Goede
2020-07-07T19:41:43Z

Hi,

On 7/7/20 9:09 PM, Uwe Kleine-König wrote:
> Hello Hans,
>
> On Tue, Jul 07, 2020 at 07:31:29PM +0200, Hans de Goede wrote:
>> On 7/7/20 9:34 AM, Uwe Kleine-König wrote:
>>> On Mon, Jul 06, 2020 at 10:53:08PM +0200, Hans de Goede wrote:
>>>> But if we do then I think closest to the truth would be:
>>>>
>>>> state->period = UINT_MAX;
>>>> state->duty_cycle = 0;
>>>
>>> I'd say state->period = 1 & state->duty_cycle = 0 is a better
>>> representation.
>>
>> But that would suggest the output is configured for an
>> infinitely high output frequency, but the frequency is
>> actually 0, the reason why get_state needs to treat a
>> base_unit val of 0 special at all is to avoid a division
>> by 0, and in math dividing by 0 gives infinite, isn't
>> UINT_MAX a better way to represent infinity ?
>
> Given that duty_cycle is 0, how can to tell anything about the period
> when only seeing the signal (= a constant low)?
>
> Given that (ideally) a period is completed when pwm_apply_state() is
> called, a short period is much more sensible.

Ok, I will add a patch to v4 of the patch-set to adjust the pwm-lpss
driver's get_state method accordingly.

Regards,

Hans