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Re: [Qemu-devel] Minimum RAM size for PC machines?

From: David Hildenbrand
Subject: Re: [Qemu-devel] Minimum RAM size for PC machines?
Date: Thu, 23 Mar 2017 10:18:28 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 23.03.2017 09:19, Gerd Hoffmann wrote:
> On Mi, 2017-03-22 at 11:19 +0100, David Hildenbrand wrote:
>> On 22.03.2017 11:03, Thomas Huth wrote:
>>> On 22.03.2017 10:08, Markus Armbruster wrote:
>>> [...]
>>>> Are we now ready to accept a simple & stupid patch that actually helps
>>>> users, say letting boards that care declare minimum and maximum RAM
>>>> size?  And make PC reject RAM size less than 1MiB, even though "someone"
>>>> might conceivably have firmware that works with less?
>>> I'd say enforce a minimum RAM size on the normal "pc" and "q35" machine,
>>> but still allow smaller sizes on the "isapc" machine. So if "someone"
>>> comes around and claims to have a legacy firmware that wants less memory
>>> than 1MiB, just point them to the isapc machine.
>>> Just my 0.02 €.
>>>  Thomas
>> Or maybe simply warn the user that things may go wrong instead of
>> enforcing it.
> Why bother?  I have my doubts physical i440fx works with less than 1M
> either, given that this memory is needed to shadow the roms.  Possibly
> you can't even find dimms that are small to plug them into such a system
> to try ...

Because it seems to work if you supply the correct rom. We are trying to
catch user errors, don't we?

> I'd say just add a hard limit and be done with it.

"640K ought to be enough for anybody". Any limit we set will become out
of date.

> Maybe exclude isapc.  That one hasn't shadow support so things have at
> least a chance to work with less than 1M of memory.  But honestly I'd
> rather drop isapc, together with ia64 and sparc.  I mean, what is the
> use case?  'pc' machine type is compatible enough with vga and ide ports
> being on the standard isa locations so even msdos which has no pci
> support at all boots happily.

I think I like that idea.

> cheers,
>   Gerd




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