We use the colibri-imx6ull SoM with a Display connected. Also we use PWM_B and PWM_C for status LEDs. While booting, BL_ON and PWM_B switch to high, effectively turning on the Backlight and one status LED.
As a workaround I set the BL_ON and the GPIO for PWM_B to 0 in U-Boot, but they still switch to high for about half a second. It seems like this happens before U-Boot is even loaded. The result is a “flashing” Display and LED. When the Button for the special boot-mode (e.g. to load the easy installer via USB) is pressed while booting, PWM_B stays low, the display backlight still turns on.
Is it possible to flash a custom internal bootloader that does not turn on the mentioned pins?