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Re: [Qemu-devel] Seabios dislikes -M isapc

From: Jamie Lokier
Subject: Re: [Qemu-devel] Seabios dislikes -M isapc
Date: Thu, 11 Feb 2010 23:51:41 +0000
User-agent: Mutt/1.5.13 (2006-08-11)

Anthony Liguori wrote:
> On 02/09/2010 06:27 PM, malc wrote:
> >APIC is almost as good as useless without ACPI and we have a switch to
> >disable that.
> >   
> Which is another thing that I'm not sure it all that useful to have.
> >>Firmware is really hard to implement if you have to deal with supporting
> >>multiple chipsets.
> >>
> >>Also, if we don't have a workload that actually needs isapc, that suggests
> >>that there's no real way to test that isapc doesn't have non-ISA things 
> >>creep
> >>into it.
> >>
> >>Given that, I'm inclined to suggest that we mark isapc as deprecated, give
> >>people some time to comment on it, and then provided that we still don't 
> >>think
> >>it's necessary, change isapc to simply use isa devices while still using 
> >>a PCI
> >>chipset.
> >>     
> >Not to comment, to give hard evidence that something is working with isapc
> >and doesn't otherwise, in which case it must stay.
> >   
> Yes.  If someone can produce a workload that requires isapc[1], I'm all 
> for continuing to support it.
> [1] Very specifically, I mean requires -M isapc to only emulate an ISA 
> bus and not emulate an ISA bus via a bridge in the PIIX chipset.  We 
> will always need an -M isapc that only uses ISA devices instead of PCI 
> devices.  However, if we can use a PCI chipset in -M isapc, we can 
> express the differences entirely via qdev.

If it emulated a PCI chipset _but_ ignored any access to the chipset
registers after the BIOS has initialised whatever it will (by
unmapping the registers but keeping the chipset device running), that
would look an awful lot like a real ISA PC at that point, wouldn't it?

-- Jamie

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