linux-kernel - [PATCH v15 3/3] pwm: sifive: fix rounding and idempotency issues in apply and get

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Message-Id: <20250529035341.51736-4-nylon.chen@sifive.com>
Date: Thu, 29 May 2025 11:53:41 +0800
From: Nylon Chen <nylon.chen@...ive.com>
To: Conor Dooley <conor@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Samuel Holland <samuel.holland@...ive.com>,
	Uwe Kleine-König <ukleinek@...nel.org>
Cc: linux-riscv@...ts.infradead.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-pwm@...r.kernel.org,
	Nylon Chen <nylon.chen@...ive.com>,
	kernel test robot <lkp@...el.com>,
	Zong Li <zong.li@...ive.com>
Subject: [PATCH v15 3/3] pwm: sifive: fix rounding and idempotency issues in apply and get_state

This fix ensures consistent rounding and avoids mismatches
between applied and reported PWM values that could trigger false
idempotency failures in debug checks

This change ensures:
- real_period is now calculated using DIV_ROUND_UP_ULL() to avoid underestimation.
- duty_cycle is rounded up to match the fractional computation in apply()
- apply() truncates the result to compensate for get_state's rounding up logic

These fixes resolve issues like:
.apply is supposed to round down duty_cycle (requested: 360/504000, applied: 361/504124)
.apply is not idempotent (ena=1 pol=0 1739692/4032985) -> (ena=1 pol=0 1739630/4032985)

Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202505080303.dBfU5YMS-lkp@intel.com/
Co-developed-by: Zong Li <zong.li@...ive.com>
Signed-off-by: Zong Li <zong.li@...ive.com>
Signed-off-by: Nylon Chen <nylon.chen@...ive.com>
---
 drivers/pwm/pwm-sifive.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
index f3694801d3ee..4a07315b0744 100644
--- a/drivers/pwm/pwm-sifive.c
+++ b/drivers/pwm/pwm-sifive.c
@@ -118,7 +118,7 @@ static void pwm_sifive_update_clock(struct pwm_sifive_ddata *ddata,
 
 	/* As scale <= 15 the shift operation cannot overflow. */
 	num = (unsigned long long)NSEC_PER_SEC << (PWM_SIFIVE_CMPWIDTH + scale);
-	ddata->real_period = div64_ul(num, rate);
+	ddata->real_period = DIV_ROUND_UP_ULL(num, rate);
 	dev_dbg(ddata->parent,
 		"New real_period = %u ns\n", ddata->real_period);
 }
@@ -143,8 +143,8 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 		state->enabled = false;
 
 	state->period = ddata->real_period;
-	state->duty_cycle =
-		(u64)duty * ddata->real_period >> PWM_SIFIVE_CMPWIDTH;
+	state->duty_cycle = DIV_ROUND_UP_ULL((u64)duty * ddata->real_period,
+					     (1U << PWM_SIFIVE_CMPWIDTH));
 	state->polarity = PWM_POLARITY_NORMAL;
 
 	return 0;
@@ -159,7 +159,8 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	unsigned long long num;
 	bool enabled;
 	int ret = 0;
-	u32 frac, inactive;
+	u64 frac;
+	u32 inactive;
 
 	if (state->polarity != PWM_POLARITY_NORMAL)
 		return -EINVAL;
@@ -178,9 +179,11 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	 * consecutively
 	 */
 	num = (u64)duty_cycle * (1U << PWM_SIFIVE_CMPWIDTH);
-	frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
+	frac = num;
+	do_div(frac, state->period);
 	/* The hardware cannot generate a 0% duty cycle */
-	frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
+	frac = min(frac, (u64)(1U << PWM_SIFIVE_CMPWIDTH) - 1);
+	/* pwmcmp register must be loaded with the inactive(invert the duty) */
 	inactive = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;
 
 	mutex_lock(&ddata->lock);
-- 
2.34.1