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intel-hda: valid registers are unknown
According to HDA specification, "3.1.2 General Register Behaviors and Access Requirements":
"All controller registers must be addressable as byte, Word, and Dword quantities."
But e.g. if you try the following to reset and enable the CORB, assuming es:esi contains the base MMIO address of the controller,
es or [esi+4bh], byte 80h ; reset CORB
corbresetloop:
es test [esi+4bh], byte 80h ; is HW done resetting yet?
jnz corbreset1ok ; yes, bit is now 1
hlt ; wait a little bit
jmp corbresetloop ; and check again
corbreset1ok:
es and [esi+4bh], byte 7fh ; clear the bit
It will hang indefinitely because the bit never gets set, and if you enable debug output of the controller with "-device intel-hda,debug=1", you will see infinitely the line "unknown register, addr 0x4b" output. The same code on a real hardware (I tried with ICH7M) works fine, as it should according to the spec.
Host/guest/version does not matter (I am writing own drivers) --- as of right now, latest version still has this code:
https://github.com/qemu/qemu/blob/master/hw/audio/intel-hda.c
which seems to emit "unknown register" message in intel_hda_reg_find(), and this function does not take into account range of addresses that each register occupies.
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