Subject: Re: [PATCH 1/1] clk: nuvoton: ma35d1: fix PLL frequency calculation

From: Joey Lu <[email-masked]>
Date: Tue, 12 May 2026 11:49:27 +0800

On 5/11/2026 11:54 PM, Brian Masney wrote:
> Hi Joey,
>
> On Mon, May 11, 2026 at 11:15:59AM +0800, Joey Lu wrote:
>> Fix four bugs in the MA35D1 PLL driver:
>>
>> 1. PLL_CTL1_FRAC was defined as GENMASK(31, 24) (8 bits), but the
>>     hardware fractional field spans bits [31:8] (24 bits). This caused
>>     wrong frequency calculation in fractional and spread-spectrum modes.
>>
>> 2. div_u64() does not modify its argument in-place; the quotient must
>>     be assigned from the return value. Both ma35d1_calc_smic_pll_freq()
>>     and ma35d1_calc_pll_freq() discarded the return value, leaving
>>     pll_freq undivided and orders of magnitude too high.
>>
>> 3. The fractional-mode calculation divided x by FIELD_MAX(PLL_CTL1_FRAC)
>>     to get 2 decimal digits. After correcting the mask to 24 bits, update
>>     the arithmetic to use 3 decimal digits with proper 24-bit fixed-point
>>     rounding.
>>
>> 4. ma35d1_clk_pll_determine_rate() called ma35d1_pll_find_closest()
>>     unconditionally before the switch, but then overwrote its result by
>>     reading the current hardware registers for every PLL type. Move the
>>     find_closest() call inside the configurable-PLL branch (APLL, EPLL,
>>     VPLL). CAPLL and DDRPLL do not support runtime rate changes and
>>     correctly return the current hardware rate.
>>
>> Fixes: 691521a367cf ("clk: nuvoton: Add clock driver for ma35d1 clock controller")
>> Signed-off-by: Joey Lu <[email-masked]>
> Thanks for the patch, however this should really be broken up into more
> patches. If possible, one patch for each of the fixes.
>
> Brian

Thanks for the feedback.🙂

I understand your point and will split the changes into several patches, 
with each patch addressing one fix.

>
>> ---
>>   drivers/clk/nuvoton/clk-ma35d1-pll.c | 34 +++++++++++++--------------
>>   1 file changed, 17 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/clk/nuvoton/clk-ma35d1-pll.c b/drivers/clk/nuvoton/clk-ma35d1-pll.c
>> index 4620acfe47e8..314b81e7727c 100644
>> --- a/drivers/clk/nuvoton/clk-ma35d1-pll.c
>> +++ b/drivers/clk/nuvoton/clk-ma35d1-pll.c
>> @@ -48,7 +48,7 @@
>>   #define PLL_CTL1_PD		BIT(0)
>>   #define PLL_CTL1_BP		BIT(1)
>>   #define PLL_CTL1_OUTDIV		GENMASK(6, 4)
>> -#define PLL_CTL1_FRAC		GENMASK(31, 24)
>> +#define PLL_CTL1_FRAC		GENMASK(31, 8)
>>   #define PLL_CTL2_SLOPE		GENMASK(23, 0)
>>   
>>   #define INDIV_MIN		1
>> @@ -92,7 +92,7 @@ static unsigned long ma35d1_calc_smic_pll_freq(u32 pll0_ctl0,
>>   	p = FIELD_GET(SPLL0_CTL0_OUTDIV, pll0_ctl0);
>>   	outdiv = 1 << p;
>>   	pll_freq = (u64)parent_rate * n;
>> -	div_u64(pll_freq, m * outdiv);
>> +	pll_freq = div_u64(pll_freq, m * outdiv);
>>   	return pll_freq;
>>   }
>>   
>> @@ -110,12 +110,12 @@ static unsigned long ma35d1_calc_pll_freq(u8 mode, u32 *reg_ctl, unsigned long p
>>   
>>   	if (mode == PLL_MODE_INT) {
>>   		pll_freq = (u64)parent_rate * n;
>> -		div_u64(pll_freq, m * p);
>> +		pll_freq = div_u64(pll_freq, m * p);
>>   	} else {
>>   		x = FIELD_GET(PLL_CTL1_FRAC, reg_ctl[1]);
>> -		/* 2 decimal places floating to integer (ex. 1.23 to 123) */
>> -		n = n * 100 + ((x * 100) / FIELD_MAX(PLL_CTL1_FRAC));
>> -		pll_freq = div_u64(parent_rate * n, 100 * m * p);
>> +		/* x is 24-bit fractional part, convert to 3 decimal digits */
>> +		n = n * 1000 + (u32)(((u64)x * 1000 + 500) >> 24);
>> +		pll_freq = div_u64((u64)parent_rate * n, 1000 * m * p);
>>   	}
>>   	return pll_freq;
>>   }
>> @@ -255,32 +255,32 @@ static int ma35d1_clk_pll_determine_rate(struct clk_hw *hw,
>>   	if (req->best_parent_rate < PLL_FREF_MIN_FREQ || req->best_parent_rate > PLL_FREF_MAX_FREQ)
>>   		return -EINVAL;
>>   
>> -	ret = ma35d1_pll_find_closest(pll, req->rate, req->best_parent_rate,
>> -				      reg_ctl, &pll_freq);
>> -	if (ret < 0)
>> -		return ret;
>> -
>>   	switch (pll->id) {
>>   	case CAPLL:
>> +	case DDRPLL:
>> +		/* Read-only PLLs: return current rate */
>>   		reg_ctl[0] = readl_relaxed(pll->ctl0_base);
>> -		pll_freq = ma35d1_calc_smic_pll_freq(reg_ctl[0], req->best_parent_rate);
>> +		if (pll->id == CAPLL) {
>> +			pll_freq = ma35d1_calc_smic_pll_freq(reg_ctl[0], req->best_parent_rate);
>> +		} else {
>> +			reg_ctl[1] = readl_relaxed(pll->ctl1_base);
>> +			pll_freq = ma35d1_calc_pll_freq(pll->mode, reg_ctl, req->best_parent_rate);
>> +		}
>>   		req->rate = pll_freq;
>> -
>>   		return 0;
>> -	case DDRPLL:
>>   	case APLL:
>>   	case EPLL:
>>   	case VPLL:
>> -		reg_ctl[0] = readl_relaxed(pll->ctl0_base);
>> -		reg_ctl[1] = readl_relaxed(pll->ctl1_base);
>> -		pll_freq = ma35d1_calc_pll_freq(pll->mode, reg_ctl, req->best_parent_rate);
>> +		/* Configurable PLLs: find closest achievable rate */
>> +		ret = ma35d1_pll_find_closest(pll, req->rate, req->best_parent_rate,
>> +					      reg_ctl, &pll_freq);
>> +		if (ret < 0)
>> +			return ret;
>>   		req->rate = pll_freq;
>> -
>>   		return 0;
>>   	}
>>   
>>   	req->rate = 0;
>> -
>>   	return 0;
>>   }
>>   
>> -- 
>> 2.49.0