Merge tag 'pwm/for-6.10-rc5-fixes-take2' of git://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/linux

Pull pwm fixes from Uwe Kleine-König:
 "Three fixes for the pwm-stm32 driver.

  The first patch prevents an integer wrap-around for small periods. In
  the second patch the calculation of the prescaler is fixed which
  resulted in values for the ARR register that don't fit into the
  corresponding register bit field. The last commit improves an error
  message that was wrongly copied from another error path"

* tag 'pwm/for-6.10-rc5-fixes-take2' of git://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/linux:
  pwm: stm32: Fix error message to not describe the previous error path
  pwm: stm32: Fix calculation of prescaler
  pwm: stm32: Refuse too small period requests

1 files changed, 16 insertions, 7 deletions

diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c
index a2f231d13a9f..8bae3fd2b330 100644
--- a/drivers/pwm/pwm-stm32.c
+++ b/drivers/pwm/pwm-stm32.c
@@ -321,22 +321,30 @@ static int stm32_pwm_config(struct stm32_pwm *priv, unsigned int ch,
 	 * First we need to find the minimal value for prescaler such that
 	 *
 	 *        period_ns * clkrate
-	 *   ------------------------------
+	 *   ------------------------------ < max_arr + 1
 	 *   NSEC_PER_SEC * (prescaler + 1)
 	 *
-	 * isn't bigger than max_arr.
+	 * 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 * priv->max_arr);
-	if (prescaler > 0)
-		prescaler -= 1;
-
+					(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
@@ -673,7 +681,8 @@ static int stm32_pwm_probe(struct platform_device *pdev)
 	 * .apply() won't overflow.
 	 */
 	if (clk_get_rate(priv->clk) > 1000000000)
-		return dev_err_probe(dev, -EINVAL, "Failed to lock clock\n");
+		return dev_err_probe(dev, -EINVAL, "Clock freq too high (%lu)\n",
+				     clk_get_rate(priv->clk));
 
 	chip->ops = &stm32pwm_ops;