qemu-system-riscv64: It cannot initialize ramfb video adapter
Host environment
- Operating system: Ubuntu 22.04.1
- OS/kernel version: 5.15.0-53-generic
- Architecture: x86_64
- QEMU flavor: qemu-riscv64
- QEMU version: QEMU emulator version 6.2.0 (Debian 1:6.2+dfsg-2ubuntu6.5)
- QEMU command line:
qemu-system-riscv64 -machine virt -kernel build/kernel -device ramfb -bios none -serial stdio
Emulated/Virtualized environment
- Operating system: Bare metal
- OS/kernel version: Bare metal
- Architecture: riscv64
Description of problem
It looks like ramfb video adapter doesn't work in riscv64 architecture. But it works fine in aarch64 architecture.
Steps to reproduce
- Launch the attached kernel with command:
qemu-system-riscv64 -machine virt -kernel kernel -device ramfb -bios none -serial stdio- You will get the messages in console:
guest fw_cfg dma-interface enabled
setup ramfb successfull- Video adapter will not initialize. QEMU window will continue display this message:
Guest has not initialized the display (yet).Additional information
There is a useful project for aarch64 architecture - https://github.com/luickk/qemu-ramfb-aarch64-driver. This is a Bare metal driver for ramfb adapter. It works fine. I adapted it for riscv64 architecture - https://github.com/CityAceE/qemu-ramfb-riscv64-driver. I've successfully went through all problems. Driver compiles now and launches. But unfortunately ramfb doesn't initialize. I parallel traced aarch64 and riscv64. They works equal until initialization. Aarch64 changes revolution just after qemu_cfg_write_entry call, but nothing happened after qemu_cfg_write_entry call in riscv64 emulation. I spent a lot of time trying to resolve this problem, but it looks like a problem in qemu-system-riscv64.
UPDATE
Tested with Windows builds of QEMU:
v 6.1 - The same situation as Ubuntu build 6.2.
v 7.1.92 - Stopped with message:
c:\Program Files\qemu\qemu-system-riscv64.exe: -device ramfb: ramfb device requires fw_cfg with DMAP.S. v 7.1.92 - qemu-system-aarch64.exe with aarch64 kernel build works fine.
UPDATE2
QEMU emulator version 7.0.0 (v7.0.0-11902-g1d935f4a02-dirty) is the last Windows build which opens my riscv64 kernel without message about requirement of fw_cfg with DMA. Next build "QEMU emulator version 7.0.90 (v7.1.0-rc0-11915-g5f9b281b8a-dirty)" already has this issue.