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@xxxxxxxxxx> ... >> /* >> + * 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
