I know that F33 is not officially supported on Raspberry Pi 4, but maybe this report will improve that situation anyway.

I'm experiencing occasional kernel panics right after GRUB, at around 6 secs into the boot process with F33 on a Raspberry Pi 4 with ethernet connected. Following is a description of the situation and what I've tried so far.

Test-Setup

Stock F33 raw image (Fedora-IoT-33-20201215.0.aarch64.raw.xz)
Unmodified Raspberry Pi 4 1 GB (with latest EEPROM Firmware)
Ethernet-Network via Fritzbox 7490 (this is important, see below)

The Issue

If and only if the network cable is connected, the boot will result in a kernel panic at around 50 - 60 % of boot attempts.

Findings so far:

• The boot works flawless on networks with Teltonika Routers (RUT950 / TRB140)
• I've a Fritzbox 7390 Network which is OK and another which causes problems
• Boot is NOK if ethernet connected until GRUB, if connected after GRUB its OK

Inspecting the EEPROM bootloader by booting without an SD card one can see that the priority is 0x41 (boot: mode SD 1 order f41 retry 0/0 restart 0/-1) which indicates that no network-boot is considered by the EEPROM bootloader, only SD card with a USB fallback - according to documentation.

The only difference in that setup observed from the (non-debug) logs between a working and non-working boot is this:

xxxx Waiting for PHY auto negotiation to complete.... TIMEOUT!
xxx PHY startup failed: -110

I have a Raspberry Pi 4 4GB Edition with works flawless in a Fritzbox 7390 Network, where problems in other Fritzbox 7390 Networks (and other networks in general) were only observed with the 1GB Edition while not tested with the 4GB edition for logistical reasons - can't rule out differences between both editions.

What's still to try

• Observe the network with tcpdump and post findings here
• Boot with debug options and post findings here
• Test if Raspberry Pi 4 4GB Edition has the same problems