I've had a HiFiBerry DAC+ RTC board on a Raspberry Pi 3A+ under old Raspbian for a while and it worked great. But now I have migrated the system to the new 64-bit Raspberry Pi OS (based on Debian GNU/Linux 11 (bullseye)) with the kernel Linux 5.15.32-v8+ aarch64 and the system does not recognize the board.
I've appended the following to /boot/config.txt on the new system:
Despite that, the card seems not to be detected. aplay does find something though:
# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: vc4hdmi [vc4-hdmi], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
Subdevice #0: subdevice #0
The board is plugged onto the GPIO headers and held down with the nylon bolts as it has been all along. That hasn't changed, just the new OS.
What steps am I missing to get sound from the HiFiBerry DAC+ RTC?