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SubjectRe: [PATCH V3] pwm: tegra: dynamic clk freq configuration by PWM driver
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On 26/05/2020 13:05, Jon Hunter wrote:
>
> On 26/05/2020 12:25, Sandipan Patra wrote:
>> Added support for dynamic clock freq configuration in pwm kernel driver.
>> Earlier the pwm driver used to cache boot time clock rate by pwm clock
>> parent during probe. Hence dynamically changing pwm frequency was not
>> possible for all the possible ranges. With this change, dynamic calculation
>> is enabled and it is able to set the requested period from sysfs knob
>> provided the value is supported by clock source.
>>
>> Changes mainly have 2 parts:
>> - T186 and later chips [1]
>> - T210 and prior chips [2]
>>
>> For [1] - Changes implemented to set pwm period dynamically and
>> also checks added to allow only if requested period(ns) is
>> below or equals to higher range.
>>
>> For [2] - Only checks if the requested period(ns) is below or equals
>> to higher range defined by max clock limit. The limitation
>> in T210 or prior chips are due to the reason of having only
>> one pwm-controller supporting multiple channels. But later
>> chips have multiple pwm controller instances each having
>> single channel support.
>>
>> Signed-off-by: Sandipan Patra <spatra@nvidia.com>

...

>> /*
>> + * Period in nano second has to be <= highest allowed period
>> + * based on max clock rate of the pwm controller.
>> + *
>> + * higher limit = max clock limit >> PWM_DUTY_WIDTH
>> + * lower limit = min clock limit >> PWM_DUTY_WIDTH >> PWM_SCALE_WIDTH
>
> Not sure why we mention the lower limit if we are not testing this
> condition. Does not appear to be relevant here. Or should we be checking
> this as well?

The above comment appears to be incorrect. Looking further at the code,
the code seems fine but the comment is confusing. I think you mean to
say that 'the period needs to be greater than the minimum period' and
that ...

min period = max clock limit >> PWM_DUTY_WIDTH
max period = min clock limit >> PWM_DUTY_WIDTH >> PWM_SCALE_WIDTH

>
>> + */
>> + if (period_ns < pc->min_period_ns)
>> + return -EINVAL;
>
> Something does not seem right here. If this is the highest allowed
> period, shouldn't this variable be called 'max_period_ns'?

Jon

--
nvpublic

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