On 2021/7/23, 3:17 AM, "Uwe Kleine-König" <u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
On Wed, Jul 21, 2021 at 10:52:21AM +0000, Billy Tsai wrote:
>> 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.
> I thought if you disable the PWM it emits the inactive level? Then this
> is the best you can do if duty_cycle = 0 is requested.
Thanks for your quick reply.
When duty_cycle = 0 is requested my driver currently will emit the inactive level.
So, the next patch I need to do is to add the comment about this?
Best Regards,
Billy Tsai
