Re: [PATCH 1/3] pwm: driver for qualcomm ipq6018 pwm block

[Baruch Siach <baruch@tkos.co.il>]

Hi test robot,

Thanks for testing and reporting.

On Tue, Feb 08 2022, kernel test robot wrote:

[snip]

>>> drivers/pwm/pwm-ipq.c:122:11: warning: result of comparison of constant 16000000000 with expression of type 'unsigned long' is always false [-Wtautological-constant-out-of-range-compare]
>            if (rate > 16ULL * GIGA)
>                ~~~~ ^ ~~~~~~~~~~~~
>    1 warning generated.

This clang warning is only enabled with W=1 (see commit
afe956c577b). Not sure how to avoid it.

Is there a way to express this condition without making clang warn on
platforms where ULONG_MAX == 2^32? Maybe cast to unsigned long long? Or
should we just ignore this W=1 warning?

baruch

> vim +122 drivers/pwm/pwm-ipq.c
>
>     99	
>    100	static int ipq_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>    101				 const struct pwm_state *state)
>    102	{
>    103		struct ipq_pwm_chip *ipq_chip = ipq_pwm_from_chip(chip);
>    104		unsigned int pre_div, pwm_div, best_pre_div, best_pwm_div;
>    105		unsigned long rate = clk_get_rate(ipq_chip->clk);
>    106		u64 period_ns, duty_ns, period_rate;
>    107		u64 min_diff;
>    108	
>    109		if (state->polarity != PWM_POLARITY_NORMAL)
>    110			return -EINVAL;
>    111	
>    112		if (state->period < DIV64_U64_ROUND_UP(NSEC_PER_SEC, rate))
>    113			return -ERANGE;
>    114	
>    115		period_ns = min(state->period, IPQ_PWM_MAX_PERIOD_NS);
>    116		duty_ns = min(state->duty_cycle, period_ns);
>    117	
>    118		/*
>    119		 * period_ns is 1G or less. As long as rate is less than 16 GHz,
>    120		 * period_rate does not overflow. Make that explicit.
>    121		 */
>  > 122		if (rate > 16ULL * GIGA)
>    123			return -EINVAL;
>    124		period_rate = period_ns * rate;
>    125		best_pre_div = IPQ_PWM_MAX_DIV;
>    126		best_pwm_div = IPQ_PWM_MAX_DIV;
>    127		/*
>    128		 * We don't need to consider pre_div values smaller than
>    129		 *
>    130		 *                              period_rate
>    131		 *  pre_div_min := ------------------------------------
>    132		 *                 NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1)
>    133		 *
>    134		 * because pre_div = pre_div_min results in a better
>    135		 * approximation.
>    136		 */
>    137		pre_div = div64_u64(period_rate,
>    138				(u64)NSEC_PER_SEC * (IPQ_PWM_MAX_DIV + 1));
>    139		min_diff = period_rate;
>    140	
>    141		for (; pre_div <= IPQ_PWM_MAX_DIV; pre_div++) {
>    142			u64 remainder;
>    143	
>    144			pwm_div = div64_u64_rem(period_rate,
>    145					(u64)NSEC_PER_SEC * (pre_div + 1), &remainder);
>    146			/* pwm_div is unsigned; the check below catches underflow */
>    147			pwm_div--;
>    148	
>    149			/*
>    150			 * Swapping values for pre_div and pwm_div produces the same
>    151			 * period length. So we can skip all settings with pre_div >
>    152			 * pwm_div which results in bigger constraints for selecting
>    153			 * the duty_cycle than with the two values swapped.
>    154			 */
>    155			if (pre_div > pwm_div)
>    156				break;
>    157	
>    158			/*
>    159			 * Make sure we can do 100% duty cycle where
>    160			 * hi_dur == pwm_div + 1
>    161			 */
>    162			if (pwm_div > IPQ_PWM_MAX_DIV - 1)
>    163				continue;
>    164	
>    165			if (remainder < min_diff) {
>    166				best_pre_div = pre_div;
>    167				best_pwm_div = pwm_div;
>    168				min_diff = remainder;
>    169	
>    170				if (min_diff == 0) /* bingo */
>    171					break;
>    172			}
>    173		}
>    174	
>    175		/* config divider values for the closest possible frequency */
>    176		config_div_and_duty(pwm, best_pre_div, best_pwm_div,
>    177				    rate, duty_ns, state->enabled);
>    178	
>    179		return 0;
>    180	}
>    181	
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org


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