Re: [Qemu-devel] [RFC] edk2 support for a new QEMU device - PXB (PCI Expander Device)

[Laszlo Ersek]

On 06/04/15 17:18, Marcel Apfelbaum wrote:
> On 06/04/2015 04:04 PM, Laszlo Ersek wrote:
>> On 06/04/15 11:42, Marcel Apfelbaum wrote:
>>> On 06/04/2015 02:11 AM, Laszlo Ersek wrote:
>>
>>>> What element type do you propose for the array in the new fw_cfg file?
>>>> (And what name for the fw_cfg file itself?)
>>>>
>>>> "etc/extra-pci-roots" uses uint64_t, little endian, for the number of
>>>> extra root buses. (In fact if you expose the explicit list in a
>>>> separate
>>>> file, then the element count is not even necessary separately, because
>>>> file sizes are available in the fw_cfg directory, and I can divide the
>>>> file size with the element size.)
>>
>>> I can prepare another file.
>>
>> As long as we're crossing neither a QEMU nor a SeaBIOS release boundary,
>> I think we could just change the contents of the same file, with the
>> existing name.
> The extra-roots file was existing before PXB.
> I am afraid to break some other thing.
> This is why I prefer another file.

Noted.

>>> Regarding the new  array, each element
>>> should be
>>> a number between 0x0 and 0xff, so a uint8_t seems fair.
>>
>> Hm. The number of bytes to save here is really small, and it has been
>> suggested to maybe try to support segments? I don't know anything about
>> PCI segments; I vaguely recall that it allows for disjoint bus
>> intervals, with each interval having at most 256 elements. Maybe we
>> could accommodate that with a uint32_t element type?

> While I dont' really care about the type,
> Pmultiple pci segments correspond to multiple *host bridges*,
> as opposed to one host bridge with multiple root bridges.

Noted. UINT8 is fine then.

Thanks!
Laszlo