Comment 83 for bug 1428121

In the case of Intel HDMI, the audio device is a kind of slave of GPU. The actual data is handled solely in the graphics side.

And, on the recent Intel chips like Haswell, both are integrated more tightly. For example, if GPU is turned off, just accessing to the audio PCI register gives kernel Oops or a hard lockup, although it looks independent in the PCI level.