Re: [PATCH for-9.0] docs/about: Mark the iaspc machine type as deprecated

[Bernhard Beschow]

Am 28. März 2024 14:09:52 UTC schrieb Mark Cave-Ayland 
<mark.cave-ayland@ilande.co.uk>:
>On 27/03/2024 07:09, Gerd Hoffmann wrote:
>
>> On Tue, Mar 26, 2024 at 01:30:48PM +0000, Mark Cave-Ayland wrote:
>>> Heh I've actually been using isapc over the past couple of weeks to fire up
>>> some old programs in a Windows 3 VM :)
>> 
>> I'm wondering why these use cases can't simply use the 'pc' machine
>> type?
>> 
>> The early pci chipsets of the 90-ies have been designed in a
>> backward-compatible manner, with devices such as the IDE controller
>> being mapped to the standard ISA ioports.  So even an historic OS which
>> does not know what PCI is can run on that hardware, by simply talking to
>> devices using the standard ISA io ports ...
>
>Hmmm that's a fair point: I think the pc machine has a PCI-ISA bridge 
>included, so ISA devices can be plugged in as needed. The reason I ended up on 
>that configuration was because I ended up chasing down a regression, and 
>wanted to quickly eliminate things such as ACPI.

In theory you could pass `-M acpi=off` to not instantiate the PIIX4 ACPI 
function, essentially turning the Frankenstein-PIIX4 SB into a PIIX3. However, 
this also removes SMI registers used by SeaBIOS to handle SMM setup which may 
create unwanted side effects. On a real PIIX3, these registers are located in 
the ISA function. I wonder if it made sense to implement that for greater 
compatibility.

What do you think? Gerd, what do you think w.r.t. SeaBIOS?

Best regards,
Bernhard

>
>
>ATB,
>
>Mark.
>
>