1 files changed, 44 insertions, 18 deletions

diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c
index 0c028d17c0..5baa487f35 100644
--- a/drivers/pwm/pwm-stm32.c
+++ b/drivers/pwm/pwm-stm32.c
@@ -309,29 +309,43 @@ unlock:
 }
 
 static int stm32_pwm_config(struct stm32_pwm *priv, unsigned int ch,
-			    int duty_ns, int period_ns)
+			    u64 duty_ns, u64 period_ns)
 {
-	unsigned long long prd, div, dty;
-	unsigned int prescaler = 0;
+	unsigned long long prd, dty;
+	unsigned long long prescaler;
 	u32 ccmr, mask, shift;
 
-	/* Period and prescaler values depends on clock rate */
-	div = (unsigned long long)clk_get_rate(priv->clk) * period_ns;
-
-	do_div(div, NSEC_PER_SEC);
-	prd = div;
-
-	while (div > priv->max_arr) {
-		prescaler++;
-		div = prd;
-		do_div(div, prescaler + 1);
-	}
-
-	prd = div;
+	/*
+	 * .probe() asserted that clk_get_rate() is not bigger than 1 GHz, so
+	 * the calculations here won't overflow.
+	 * First we need to find the minimal value for prescaler such that
+	 *
+	 *        period_ns * clkrate
+	 *   ------------------------------ < max_arr + 1
+	 *   NSEC_PER_SEC * (prescaler + 1)
+	 *
+	 * This equation is equivalent to
+	 *
+	 *        period_ns * clkrate
+	 *   ---------------------------- < prescaler + 1
+	 *   NSEC_PER_SEC * (max_arr + 1)
+	 *
+	 * Using integer division and knowing that the right hand side is
+	 * integer, this is further equivalent to
+	 *
+	 *   (period_ns * clkrate) // (NSEC_PER_SEC * (max_arr + 1)) ≤ prescaler
+	 */
 
+	prescaler = mul_u64_u64_div_u64(period_ns, clk_get_rate(priv->clk),
+					(u64)NSEC_PER_SEC * ((u64)priv->max_arr + 1));
 	if (prescaler > MAX_TIM_PSC)
 		return -EINVAL;
 
+	prd = mul_u64_u64_div_u64(period_ns, clk_get_rate(priv->clk),
+				  (u64)NSEC_PER_SEC * (prescaler + 1));
+	if (!prd)
+		return -EINVAL;
+
 	/*
 	 * All channels share the same prescaler and counter so when two
 	 * channels are active at the same time we can't change them
@@ -351,8 +365,8 @@ static int stm32_pwm_config(struct stm32_pwm *priv, unsigned int ch,
 	regmap_set_bits(priv->regmap, TIM_CR1, TIM_CR1_ARPE);
 
 	/* Calculate the duty cycles */
-	dty = prd * duty_ns;
-	do_div(dty, period_ns);
+	dty = mul_u64_u64_div_u64(duty_ns, clk_get_rate(priv->clk),
+				  (u64)NSEC_PER_SEC * (prescaler + 1));
 
 	regmap_write(priv->regmap, TIM_CCR1 + 4 * ch, dty);
 
@@ -656,6 +670,18 @@ static int stm32_pwm_probe(struct platform_device *pdev)
 
 	stm32_pwm_detect_complementary(priv);
 
+	ret = devm_clk_rate_exclusive_get(dev, priv->clk);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to lock clock\n");
+
+	/*
+	 * With the clk running with not more than 1 GHz the calculations in
+	 * .apply() won't overflow.
+	 */
+	if (clk_get_rate(priv->clk) > 1000000000)
+		return dev_err_probe(dev, -EINVAL, "Clock freq too high (%lu)\n",
+				     clk_get_rate(priv->clk));
+
 	chip->ops = &stm32pwm_ops;
 
 	/* Initialize clock refcount to number of enabled PWM channels. */