linux-kernel - [PATCH v6 10/10] pwm: dwc: use clock rate in hz to avoid rounding issues

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Message-Id: <20221020151610.59443-11-ben.dooks@sifive.com>
Date:   Thu, 20 Oct 2022 16:16:10 +0100
From:   Ben Dooks <ben.dooks@...ive.com>
To:     linux-pwm@...r.kernel.org
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lee Jones <lee.jones@...aro.org>,
        u.kleine-koenig@...gutronix.de,
        Thierry Reding <thierry.reding@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Greentime Hu <greentime.hu@...ive.com>,
        jarkko.nikula@...ux.intel.com,
        William Salmon <william.salmon@...ive.com>,
        Jude Onyenegecha <jude.onyenegecha@...ive.com>,
        Ben Dooks <ben.dooks@...ive.com>
Subject: [PATCH v6 10/10] pwm: dwc: use clock rate in hz to avoid rounding issues

As noted, the clock-rate when not a nice multiple of ns is probably
going to end up with inacurate caculations, as well as on a non pci
system the rate may change (although we've not put a clock rate
change notifier in this code yet) so we also add some quick checks
of the rate when we do any calculations with it.

Signed-off-by; Ben Dooks <ben.dooks@...ive.com>
Reported-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
 drivers/pwm/pwm-dwc-of.c |  2 +-
 drivers/pwm/pwm-dwc.c    | 29 ++++++++++++++++++++---------
 drivers/pwm/pwm-dwc.h    |  2 +-
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/drivers/pwm/pwm-dwc-of.c b/drivers/pwm/pwm-dwc-of.c
index c5b4351cc7b0..5f7f066859d4 100644
--- a/drivers/pwm/pwm-dwc-of.c
+++ b/drivers/pwm/pwm-dwc-of.c
@@ -50,7 +50,7 @@ static int dwc_pwm_plat_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, PTR_ERR(dwc->clk),
 				     "failed to get timer clock\n");
 
-	dwc->clk_ns = NSEC_PER_SEC / clk_get_rate(dwc->clk);
+	dwc->clk_rate = clk_get_rate(dwc->clk);
 	return devm_pwmchip_add(dev, &dwc->chip);
 }
 
diff --git a/drivers/pwm/pwm-dwc.c b/drivers/pwm/pwm-dwc.c
index 5ef0fe7ea3e9..f48a6245a3b5 100644
--- a/drivers/pwm/pwm-dwc.c
+++ b/drivers/pwm/pwm-dwc.c
@@ -43,18 +43,22 @@ static int __dwc_pwm_configure_timer(struct dwc_pwm *dwc,
 	u32 high;
 	u32 low;
 
+	if (dwc->clk)
+		dwc->clk_rate = clk_get_rate(dwc->clk);
+
 	/*
 	 * Calculate width of low and high period in terms of input clock
 	 * periods and check are the result within HW limits between 1 and
 	 * 2^32 periods.
 	 */
-	tmp = DIV_ROUND_CLOSEST_ULL(state->duty_cycle, dwc->clk_ns);
+	tmp = state->duty_cycle * dwc->clk_rate;
+	tmp = DIV_ROUND_CLOSEST_ULL(tmp, NSEC_PER_SEC);
 	if (tmp < 1 || tmp > (1ULL << 32))
 		return -ERANGE;
 	low = tmp - 1;
 
-	tmp = DIV_ROUND_CLOSEST_ULL(state->period - state->duty_cycle,
-				    dwc->clk_ns);
+	tmp = (state->period - state->duty_cycle) * dwc->clk_rate;
+	tmp = DIV_ROUND_CLOSEST_ULL(tmp, NSEC_PER_SEC);
 	if (tmp < 1 || tmp > (1ULL << 32))
 		return -ERANGE;
 	high = tmp - 1;
@@ -120,6 +124,7 @@ static void dwc_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 			      struct pwm_state *state)
 {
 	struct dwc_pwm *dwc = to_dwc_pwm(chip);
+	unsigned long clk_rate;
 	u64 duty, period;
 	u32 ctrl, ld, ld2;
 
@@ -129,22 +134,28 @@ static void dwc_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 	ld = dwc_pwm_readl(dwc, DWC_TIM_LD_CNT(pwm->hwpwm));
 	ld2 = dwc_pwm_readl(dwc, DWC_TIM_LD_CNT2(pwm->hwpwm));
 
+	if (dwc->clk)
+		dwc->clk_rate = clk_get_rate(dwc->clk);
+
+	clk_rate = dwc->clk_rate;
 	state->enabled = !!(ctrl & DWC_TIM_CTRL_EN);
 
 	/* If we're not in PWM, technically the output is a 50-50
 	 * based on the timer load-count only.
 	 */
 	if (ctrl & DWC_TIM_CTRL_PWM) {
-		duty = (ld + 1) * dwc->clk_ns;
-		period = (ld2 + 1)  * dwc->clk_ns;
+		duty = ld + 1;
+		period = ld2 + 1;
 		period += duty;
 	} else {
-		duty = (ld + 1) * dwc->clk_ns;
+		duty = ld + 1;
 		period = duty * 2;
 	}
 
-	state->period = period;
-	state->duty_cycle = duty;
+	duty *= NSEC_PER_SEC;
+	period *= NSEC_PER_SEC;
+	state->period = DIV_ROUND_CLOSEST_ULL(period, clk_rate);
+	state->duty_cycle = DIV_ROUND_CLOSEST_ULL(duty, clk_rate);
 	state->polarity = PWM_POLARITY_INVERSED;
 
 	pm_runtime_put_sync(chip->dev);
@@ -164,7 +175,7 @@ struct dwc_pwm *dwc_pwm_alloc(struct device *dev)
 	if (!dwc)
 		return NULL;
 
-	dwc->clk_ns = 10;
+	dwc->clk_rate = NSEC_PER_SEC / 10;
 	dwc->chip.dev = dev;
 	dwc->chip.ops = &dwc_pwm_ops;
 	dwc->chip.npwm = DWC_TIMERS_TOTAL;
diff --git a/drivers/pwm/pwm-dwc.h b/drivers/pwm/pwm-dwc.h
index dc451cb2eff5..19bdc2224690 100644
--- a/drivers/pwm/pwm-dwc.h
+++ b/drivers/pwm/pwm-dwc.h
@@ -41,7 +41,7 @@ struct dwc_pwm {
 	struct pwm_chip chip;
 	void __iomem *base;
 	struct clk *clk;
-	unsigned int clk_ns;
+	unsigned long clk_rate;
 	struct dwc_pwm_ctx ctx[DWC_TIMERS_TOTAL];
 };
 #define to_dwc_pwm(p)	(container_of((p), struct dwc_pwm, chip))
-- 
2.35.1