Re: [Qemu-devel] vga-pci and MMIO BAR

[Avi Kivity]

On 07/25/2012 01:53 PM, Benjamin Herrenschmidt wrote:
> On Wed, 2012-07-25 at 13:27 +0300, Avi Kivity wrote:
>> On 07/25/2012 06:57 AM, Benjamin Herrenschmidt wrote:
>> > Hi folks !
>> > 
>> > Would there be any objection to adding a second MMIO BAR to qemu-vga
>> > which mirrors the bochs magic VBE ports ?
>> > 
>> > Support for IO space is optional in PCIe and can be problematic on some
>> > architectures, it would be nice to be able to program the card entirely
>> > using mmio.
>> 
>> Can we choose a PCIe chipset that does support IO space?
> 
> Why bother ? It's not like mode setting is performance critical and IO
> space is always going to be a pain on non-x86 ...

For compatibility?  If it's a special pain, then I understand, but
what's the difference between emulating chipset A or B?

> 
>> If not, we can add a second BAR, but it should disappear when running an
>> older machine type.
> 
> Well, the IO ports in legacy space are still there. We can also make the
> "register BAR" exist in both mode or we can add a second BAR and have
> x86 "prefer" IO... whatever rocks your boat as long as it's a BAR, it's
> the legacy hole that's annoying for me :-)

A guest created with -M old must look exactly the same as it did in an
older version of qemu, no extra BARs.


-- 
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