Re: [Qemu-devel] [PATCH v6 7/7] hw/pci-bridge: format SeaBIOS-compliant OFW device node for PXB

[Laszlo Ersek <lersek@redhat.com>]

On 06/17/15 21:32, Michael S. Tsirkin wrote:
> On Wed, Jun 17, 2015 at 03:28:44PM -0400, Kevin O'Connor wrote:
>> On Wed, Jun 17, 2015 at 09:15:24PM +0200, Laszlo Ersek wrote:
>>> On 06/17/15 20:54, Michael S. Tsirkin wrote:
>>>> Right. But what I was discussing is a different issue.  The point is
>>>> that it does not make sense to have /pci@i0cf8 under two hierarchies:
>>>> it's the same register.  What happens is that you access /pci@i0cf8 and
>>>> then *through that* you access another pci root.  Not the other way
>>>> around.  The proposal thus is to switch to /pci@i0cf8/pci-root@N in
>>>> seabios,
>>>
>>> For me this is still Question 1 -- 'everything in that pattern that is
>>> not "N"'.
>>>
>>> You seem to care about the *semantics* of that OFW device path fragment.
>>> I don't. First, the relevant IEEE spec is prohibitively hard for me to
>>> interpret semantically. Second, there is no known firmware that actually
>>> looks at the "i0cf8" unit-address term and decides *based on that term*
>>> that it has to talk PCI via 0xCF8 and 0xCFC. In other words, the current
>>> second node is entirely opaque in my interpretation.
>>>
>>>> unconditionally - not if (QEMU).
>>>
>>> This might qualify as some kind of semantic cleanup, but it will
>>> nonetheless break the SeaBIOS boot options expressed in OFW notation
>>> that are already persistently stored in cbfs, on physical machines. (As
>>> far as I understood.) It might not break the Coreboot-SeaBIOS interface,
>>> but it might invalidate preexistent entries that exist in the prior form
>>> (wherever they exist on physical hardware).
>>>
>>>> And I thought Kevin agreed
>>>> it's a good idea.
>>>>
>>>> Kevin - is this a good summary of your opinion?
>>>
>>> Kevin, please do answer.
>>
>> It is true that it would "invalidate preexistent entries" for
>> coreboot/seabios users that upgrade, but I think that is manageable.
>> So I defer the syntax discussion and decisions to the QEMU developers
>> that are doing the bulk of the work.
>>
>> -Kevin
> 
> I'm fine with either /pci@i0cf8,%x or /pci-root@%x/pci@i0cf8, with a
> slight preference to the later - in particular it's easier
> to implement in QEMU.
> 
> It means old bios won't boot from a pxb, but I think that's
> manageable - it works otherwise.

I don't understand -- the second option you named
("/pci-root@%x/pci@i0cf8") is what this patch implements, and "old" (ie.
current) SeaBIOS does boot from it.

Laszlo