[PATCH] pwm: stm32: add comment to better describe breakinput feature

[Fabrice Gasnier]

Add a comment to better describe the purpose of breakinput feature that
can be found on some STM32 timer instances. Briefly comment on the
characteristics of this input for PWM, and pinmuxing as suggested in [1].

[1] https://lkml.org/lkml/2019/10/1/207

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx>
---
 drivers/pwm/pwm-stm32.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c
index 359b085..6406ebb 100644
--- a/drivers/pwm/pwm-stm32.c
+++ b/drivers/pwm/pwm-stm32.c
@@ -522,8 +522,14 @@ static int stm32_pwm_apply_breakinputs(struct stm32_pwm *priv,
 					     sizeof(struct stm32_breakinput));
 
 	/*
+	 * Some timer instances can have BRK input pins (e.g. basically a fault
+	 * pin from the output power stage). The break feature allows a safe
+	 * shut-down of the PWM outputs to a predefined state. Further details
+	 * are available in application note AN4277, "Using STM32 device PWM
+	 * shut-down features..."
 	 * Because "st,breakinput" parameter is optional do not make probe
-	 * failed if it doesn't exist.
+	 * failed if it doesn't exist. The pinctrl handle must hold the BRK
+	 * pin(s) when using "st,breakinput" property.
 	 */
 	if (nb <= 0)
 		return 0;
-- 
2.7.4