Backlight PWM Behavior Discrepancy Between BSP 2.6 and 2.7

Technical Support
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1

Hey,

I wanted to bring to your attention a notable change in behavior regarding the backlight PWM in the Toradex Board Support Package (BSP) versions 2.6 and 2.7.

In BSP 2.6, the backlight PWM remained active during shutdown. However, with the update to BSP 2.7, we’ve observed that the backlight PWM is now being turned off during shutdown.

This change in behavior might affect certain applications or setups where the backlight PWM state during shutdown is crucial.

If you’ve encountered this change and have insights or workarounds to share, please feel free to contribute to this discussion. Your experiences and solutions could be beneficial to others navigating this adjustment.

Colibri iMX6DL 512MB IT V1.1A
Linux BSP 2.7

Looking forward to hearing your thoughts and experiences!

Best regards,
Bob

2

Hello @Bob , welcome to the community :slight_smile:

As you might be aware, BSP 2.6 and 2.7 are in EOL state since a long time.

Could you please elaborate more on that? If this is your use case, could you please describe it in detail?

Best regards,
Josep

3

Hello @Josep

Currently we cannot update to a BSP newer than 2.7. After the machine is shut down, the user is presented with a “power off screen” indicating that the power can/must be turned off now. To do this, the backlight PWM must remain switched on when the shutdown-target becomes active. This was the case with BSP 2.6. What exactly has changed regarding the backlight PWM?

// enable backlight pwm
echo 0 > /sys/class/backlight/backlight/bl_power #0 : bright

Locking forward to hear from you.

Best regards,
Bob

4

Hi @Bob !

Could you elaborate on this? Since you are using Colibri iMX6, you can use it on your module.

As already said, BSP 2.7 is from 6~7 years ago. Have you checked the Systemd service sequence?

Best regards,

5

Hello

The changed behaviour is because of:
The backlight driver used within BSP2.7 has a shutdown function, which the BSP2.6 did not have.

https://git.toradex.com/cgit/linux-toradex.git/diff/drivers/video/backlight/pwm_bl.c?h=toradex_4.1-2.0.x-imx&id=5f33b896246a2d9bdf01352de11d4dab96ba2fc9

We decided to revert this commit. To get back the power off screen after shutdown.

Best regards,
Bob