dts: bindings : explains the flag for stm32 complementary channel

Depending on the stm32 mcus and the timer instance, several channels
can enable the complementary output for the PWM signal.
Example of a DTS <&pwm1 2 4 (PWM_POLARITY_NORMAL | PWM_COMPLEMENTARY)>;
Note that the timer channel must support the complementary output
on that channel : usually channels 1-3 + channel 4 on stm32g4x.

Signed-off-by: Francois Ramu <[email protected]>

Author: FRASTM

dts/bindings/pwm/st,stm32-pwm.yaml

@@ -26,9 +26,15 @@ properties:
 
     "#pwm-cells":
       const: 3
+      description: |
+        Number of items to expect in a PWM
+        - channel of the timer used for PWM
+        - period to set in ns
+        - flags : combination of standard flags like PWM_POLARITY_NORMAL
+          or specific flags like PWM_STM32_COMPLEMENTARY. As an example for channel2:
+           <&pwm1 2 100 (PWM_POLARITY_NORMAL | PWM_STM32_COMPLEMENTARY)>;
 
 pwm-cells:
   - channel
-# period in terms of nanoseconds
   - period
   - flags