Hi Uwe,
On 2021/7/16, 6:13 PM, "Uwe Kleine-König" <u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
On Fri, Jul 16, 2021 at 09:22:22AM +0000, Billy Tsai wrote:
>> On 2021/7/16, 3:10 PM, "Uwe Kleine-König" <u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
>>
>> On Fri, Jul 16, 2021 at 01:48:20AM +0000, Billy Tsai wrote:
>> >> On 2021/7/15, 11:06 PM, "Uwe Kleine-König" <u.kleine-koenig@xxxxxxxxxxxxxx>> wrote:
>> >> > Another is: The PWM doesn't support duty_cycle 0, on such a request the
>> >> > PWM is disabled which results in a constant inactive level.
>> >>
>> >> > (This is correct, is it? Or does it yield a constant 0 level?)
>> >>
>> >> Our pwm can support duty_cycle 0 by unset CLK_ENABLE.
>>
>> > This has a slightly different semantic though. Some consumer might
>> > expect that the following sequence:
>>
>> > pwm_apply(mypwm, { .period = 10000, .duty_cycle = 10000, .enabled = true })
>> > pwm_apply(mypwm, { .period = 10000, .duty_cycle = 0, .enabled = true })
>> > pwm_apply(mypwm, { .period = 10000, .duty_cycle = 10000, .enabled = true })
>>
>> > results in the output being low for an integer multiple of 10 µs. This
>> > isn't given with setting CLK_ENABLE to zero, is it? (I didn't recheck,
>> > if the PWM doesn't complete periods on reconfiguration this doesn't
>> > matter much though.)
>> Thanks for the explanation.
>> Our hardware actually can only support duty from 1/256 to 256/256.
>> For this situation I can do possible solution:
>> We can though change polarity to meet this requirement. Inverse the pin and use
>> duty_cycle 100.
>> But I think this is not a good solution for this problem right?
> If this doesn't result in more glitches that would be fine for me.
> (Assuming it is documented good enough in the code to be
> understandable.)
> The polarity of our pwm controller will affect the duty cycle range:
> PWM_POLARITY_INVERSED : Support duty_cycle from 0% to 99%
> PWM_POLARITY_NORMAL: Support duty_cycle from 1% to 100%
> Dynamic change polarity will result in more glitches. Thus, this will become
> a trade-off between 100% and 0% duty_cycle support for user to use our pwm device.
> I will document it and send next patch.
For handling the situation that the user want to set the duty cycle to 0%, the driver can:
1. Just return the error.
2. Use the minimum duty cycle value.
I don't know which solution will be the better way or others.
I would be grateful if you can give me some suggestion about this problem.
Thanks
Best Regards,
Billy Tsai
