Re: [Qemu-devel] IO port 0x61 is multiple used

[Jan Kiszka]

On 2015-03-19 12:41, Gerd Hoffmann wrote:
> On Di, 2015-03-17 at 15:11 +0800, Gonglei wrote:
>> On 2015/3/15 20:49, Weidong Huang wrote:
>>> Hi ALL:
>>>
>>> IO port 0x61 is used by pc speaker and NMI reason port.
>>>
>>> This is ambiguous. How to distinguish in QEMU?

That register is a mess functionality-wise because it serves multiple
hardware units that are at least logically separated - legacy. In QEMU,
the speaker emulation adopted it as it is the only unit that actually
has some functionality behind the bits (see below).

>>>
>>> I see that NMI reason port is not realized in QEMU.
>>>
>>> But linux guest will access this port to determine what the NMI reason code 
>>> means.
>>>
>>> It will access pc speaker's io port. Is this a bug?
>>>
>> Gerd, any thoughts?
> 
> Not my area of expertise, but can qemu send NMIs to the guest in the
> first place?

QEMU doesn't generate the kind of NMI events that would normally be
reported via the status bits in port 0x61. Therefore, bits 6 and 7 will
always remain unset for now.

Jan

PS: The port name shown in "info mtree" is wrong. Will send a trivial
fix to help identifying the device model behind it.

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