Radeon HDMI audio

I installed FreeBSD on a machine I am planning to use as HTPC but at one point ran into an issue where I could not get single beep out of HDMI output. No matter what I did until I found that
/usr/src/sys/dev/drm2/radeon/radeon_drv.c contains
int radeon_audio = 0
and after changing it to
int radeon_audio = 1
and re-compiling the kernel, Radeon HDMI audio started working perfectly.

I am curious, is there some particular reason why this integer has zero value and thus by default Radeon HDMI audio is literally being "turned off"? It seems to work just fine now. Does it work only for some Radeons and for others not? Or is there something else involved?

My HTPC has Radeon HD6290 ('Wrestler') in it.