My goal is to get an u-boot -> iPXE over iSCSI booted rock 
stable Edge-V box using the bare minimum kernel driver and devices by tweaking dtb. ATM I am new in this area and I kindly ask if there are solutions in place to moving forward on this topic.
After executing dmesg --level=err I got a list of kernel errors, some of them are known, other I have no clue:
[ 1.296244] rockchip-pcie f8000000.pcie: PCIe link training gen1 timeout!
[ 1.301868] rk-vcodec ff650000.vpu_service: could not find power_model node
[ 1.306248] rk-vcodec ff660000.rkvdec: could not find power_model node
[ 1.320159] rockchip-pinctrl pinctrl: pin gpio4-19 already requested by fiq-debugger; cannot claim for ff1a0000.serial
[ 1.321161] rockchip-pinctrl pinctrl: pin-147 (ff1a0000.serial) status -22
[ 1.321805] rockchip-pinctrl pinctrl: could not request pin 147 (gpio4-19) from group uart2c-xfer on device rockchip-pinctrl
[ 1.322854] dw-apb-uart ff1a0000.serial: Error applying setting, reverse things back
[ 1.334963] mali ff9a0000.gpu: Failed to get regulator
[ 1.335476] mali ff9a0000.gpu: Power control initialization failed
[ 1.351364] rk_gmac-dwmac fe300000.ethernet: cannot get clock clk_mac_speed
[ 1.502617] rockchip-dwc3 usb0: failed to get drvdata dwc3
[ 1.507810] rockchip-dwc3 usb1: fail to get drvdata hcd
[ 1.678978] rk_tsadcv2_temp_to_code: Invalid conversion table: code=1023, temperature=2147483647
[ 1.713427] vccio_sd: unsupportable voltage range: 3300000-3000000uV
[ 1.773312] rockchip-dmc dmc: Failed to get leakage
[ 1.773849] rockchip-dmc dmc: Failed to get pvtm
[ 1.774626] rockchip-dmc dmc: failed to get vop bandwidth to dmc rate
[ 1.775477] rockchip-dmc dmc: could not find power_model node
[ 1.802071] Error: Driver 'ov4689' is already registered, aborting...
[ 1.802933] Error: Driver 'ov13850' is already registered, aborting...
[ 1.810216] rockchip-vop ff900000.vop: missing rockchip,grf property
[ 1.811775] rockchip-vop ff8f0000.vop: missing rockchip,grf property
[ 1.813598] i2c i2c-9: of_i2c: modalias failure on /hdmi@ff940000/ports
[ 1.819211] i2c i2c-10: of_i2c: modalias failure on /dp@fec00000/ports
[ 2.202559] rk-hdmi-dp-sound hdmi-dp-sound: control 3:0:0:ELD:0 is already present
[ 2.207006] hdmi-audio-codec hdmi-audio-codec.7.auto: ASoC: Failed to add ELD: -16
[ 3.813478] cgroup: cgroup2: unknown option "nsdelegate"
[ 5.311446] systemd[1]: Failed to start Load Kernel Modules.
[ 6.332155] midgard_kbase: exports duplicate symbol _mali_profiling_control (owned by kernel)
[ 8.280518] CONFIG-ERROR) dhd_conf_set_intiovar: txbf setting failed -23
Where can I read more about tweaking fenix, u-boot, dtb, … and deep dive into it?