Migrate virtio-rng from semu

[Charlie-Tsai1123]

Summary

This PR migrates virtio-rng support from semu while following the existing virtio-blk integration in rv32emu.

The implementation adds a virtio-rng device model, MMIO routing, PLIC interrupt integration, dynamic DTB node creation, and a new -x vrng option for system emulation mode. The guest Linux configuration is also updated to enable the virtio-rng driver so /dev/hwrng can be exposed inside the guest.

Implementation notes

• Add virtio-rng MMIO register handling, feature negotiation, queue setup, QueueNotify handling, used ring update, interrupt status handling, and device reset handling.
• Add MMIO_VIRTIORNG routing and update virtio-rng interrupts through the PLIC.
• Add vrng_new() / vrng_delete() following the existing device lifecycle style.
• Add -x vrng to enable virtio-rng at runtime.
• Dynamically create a virtio,mmio DTB node for virtio-rng when enabled.
• Enable the Linux hardware random framework and virtio-rng driver in the guest config.

Test

Build and basic check

make build-linux-image
make system_defconfig
make ENABLE_SYSTEM=1

build/rv32emu \
  -k build/linux-image/Image \
  -i build/linux-image/rootfs.cpio \
  -x vrng

Guest Verification

# cat /sys/bus/virtio/devices/virtio0/device
0x0004
# cat /sys/bus/virtio/devices/virtio0/vendor
0x12345678
# readlink /sys/bus/virtio/devices/virtio0/driver
../../../../../bus/virtio/drivers/virtio_rng
# ls -l /dev/hwrng
crw-------    1 root     root       10, 183 Jan  1  1970 /dev/hwrng
# dd if=/dev/hwrng bs=16 count=1 | hexdump -C
1+0 records in
1+0 records out
00000000  2c 9f e4 1a 6f ee c5 d8  1f fb ed bc e8 25 3a 59  |,...o........%:Y|
00000010
# dd if=/dev/hwrng bs=16 count=1 | hexdump -C
1+0 records in
1+0 records out
00000000  e9 f8 28 82 7b 66 ee bc  01 e4 9a 41 02 4a 3c f9  |..(.{f.....A.J<.|
00000010

Also tested virtio-rng together with virtio-blk:

mkdir -p build/disks
dd if=/dev/zero of=build/disks/disk.img bs=4M count=32
mkfs.ext4 -F build/disks/disk.img

build/rv32emu \
  -k build/linux-image/Image \
  -i build/linux-image/rootfs.cpio \
  -x vblk:build/disks/disk.img \
  -x vrng

Guest Verification:

# ls /sys/bus/virtio/devices
virtio0  virtio1
# cat /sys/bus/virtio/devices/virtio0/device
0x0004
# cat /sys/bus/virtio/devices/virtio1/device
0x0002
# readlink /sys/bus/virtio/devices/virtio0/driver
../../../../../bus/virtio/drivers/virtio_rng
# readlink /sys/bus/virtio/devices/virtio1/driver
../../../../../bus/virtio/drivers/virtio_blk

---

Summary by cubic

Adds virtio-rng to system emulation, exposing a guest /dev/hwrng. Implements MMIO routing, PLIC interrupts, a DTB virtio,mmio node with assigned MMIO base and IRQ, and a new -x vrng flag; coexists with virtio-blk.

• New Features

  • Virtio RNG device model (feature negotiation, queue/notify, used ring, interrupts, reset).
  • MMIO routing via MMIO_VIRTIORNG with PLIC updates (emu_update_vrng_interrupts).
  • Dynamic DTB node for virtio-rng after existing virtio-blk nodes (assigns MMIO base and IRQ).
  • New -x vrng CLI flag; guest config enables CONFIG_HW_RANDOM and CONFIG_HW_RANDOM_VIRTIO.

• Bug Fixes

  • Correct vblk MMIO range upper bound (vblk_mmio_max_hi = base + cnt - 1) to ensure proper address matching when virtio-rng is enabled.

^{Written for commit efcf2f8. Summary will update on new commits. Review in cubic}

[shengwen-tw]

Hi @Charlie-Tsai1123,

Could you add me as a co-author in the commit? AFAIK, semu may be frozen in the future.

Co-authored-by: Shengwen Cheng <shengwen1997.tw@gmail.com>

Thanks.

[Charlie-Tsai1123]

Thanks for the reminder.

[jserv]

Benchmarks

Details

Benchmark suite	Current: efcf2f8	Previous: 60f74c0	Ratio
Dhrystone	1454.667 DMIPS	1769 DMIPS	1.22
CoreMark	1060.317 iterations/sec	1153.875 iterations/sec	1.09

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