Hacks, hints, and tricks
A resting place for important technotes that don't fit anywhere else.
The kernel will lock I2C devices, making it impossible to use userspace tools to debug an issue. To get around this, modify drivers/i2c/i2c-dev.c and remove the EBUSY return statement. E.g. there's a function that either returns 0 or -EBUSY, make it always return 0.
Then you can use the i2c utilities to access devices that are in use.
Linux kernel debugfs
contains helpful debugging infos. To mount this, use this command (assuming you've compiled in said support):
mount -tdebugfs none /sys/kernel/debug
Using a serial port
To use a plug-in USB serial port with screen, you need to be part of the "dialup" group.
And add your username to the end of the "dialup" line
sudo vigr -s
And add your username yet again to the end of the "dialup" line
Exit, and log back in. You should be able to do something like
screen /dev/ttyUSB0 115200
and use the USB serial adapter you just plugged in.