Fortunately I found a low hanging fruit elsewhere: In addition to the main block of GPIOs the RPi4 also seems to have a “GPIO expansion” that hosts 8 additional GPIOs used by the firmware (the expansion also seems to be accessed via I2C). One of these GPIOs is CAM_GPIO, i.e. a pin used to turn a potentially connected camera on/off. I’ll never connect a camera to my RPi4 so this is the GPIO that I’ve been looking for. Even more conveniently the signal can be patched into easily since the camera connector has nice big (for a RPi4) pads to solder to. Works perfectly 🙂 (PS: I blacklisted the camera driver just in case..)
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