[Qemu-devel] Re: [PATCH 4/4] i8254: convert to qdev

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-03-06 18:47, Anthony Liguori wrote:
> On 03/06/2011 10:47 AM, Blue Swirl wrote:
>>> The PIT is not an ISA device.  Modelling it as such is worse than
>>> leaving it
>>> unmodelled.
>>>      
>> No. These days, PIT is part of Super I/O chip, which is accessed via
>> LPC bus. LPC is from software point of view equal to ISA. Therefore,
>> in absence of LPC, ISA is correct.
>>    
> 
> In the system we model, the PIT is part of the PIIX3.  The right way to
> model it is as a DeviceState that's no_user=1 and created as part of the
> initialized of PIIX3 (for the PC at least).
> 
> LPC is still an expansion bus and it's primarily used for discrete
> components like a TPM.  For components that are all part of a Super I/O
> chip, there really just isn't a bus in the middle.

There surely is some bus (or even multiple), just not external an one.

Most of the currently ISA-attached devices are chipset internal. They
belong to the PIIX3, so they need to be attached to some bus that is
owned by this device. If that is its ISA bus or a separate one for
internal devices - really, this looks like an academic discussion to me.

Jan


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