The raspberry pi 4B uses BCM2711 as the SOC, and the relevant file directory is in device/soc/broadcom/bcm2711.
The hardware folder contains display related files, GPU driver files, and wifi drivers files.
- device_board_soc_broadcom/hardware/display
- device_board_soc_broadcom/hardware/gpu
- device/soc/broadcom/hardware/wifi
The common folder contains the image packaging tool ptgen.c.