Re: [PATCH v6 2/4] pwm: opencores: Add PWM driver support

[William Qiu]

On 2023/10/20 19:25, Uwe Kleine-König wrote:
>> +	void __iomem *base = pwm->data->get_ch_base ?
>> +			     pwm->data->get_ch_base(pwm->regs, dev->hwpwm) : pwm->regs;
>> +	u32 period_data, duty_data, ctrl_data;
>> +
>> +	period_data = readl(REG_OCPWM_LRC(base));
>> +	duty_data = readl(REG_OCPWM_HRC(base));
>> +	ctrl_data = readl(REG_OCPWM_CTRL(base));
>> +
>> +	state->period = DIV_ROUND_CLOSEST_ULL((u64)period_data * NSEC_PER_SEC, pwm->clk_rate);
>> +	state->duty_cycle = DIV_ROUND_CLOSEST_ULL((u64)duty_data * NSEC_PER_SEC, pwm->clk_rate);
> 
> Please test your driver with PWM_DEBUG enabled. The rounding is wrong
> here.
> 

Hi Uwe,

The conclusion after checking is: when the period or duty_cycle value set
by the user is not divisible (1000000000/49.5M), there will be an error.
This error is due to hardware accuracy. So why is rounding is wrong?
rockchip also has a similar implementation drivers/pwm/ pwm-rockchip.c

Best regards,
William