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

[Laszlo Ersek]

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.

> 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?

In any case I'll leave it to you. I'll simply make the element type a
typedef in the OVMF code, and then I can easily flip it to another
integer type if necessary. One thing we should agree upon though that
whatever the width, it should be little endian.

>> I have two more questions (raised earlier), about the _HID and the _UIDs
>> in the SSDT.
>>
>> First, I can see in your patch
>>
>>    hw/acpi: add support for i440fx 'snooping' root busses
>>
>> that the _UID is populated for each root bus with a string of the form
>>
>>    PC%02X
>>
>> where the argument is "bus_num". UEFI can accommodate this, with the
>> Expanded ACPI Device Path node, but I'll have to know if the "bus_num"
>> argument matches the exact numer that you're going to pass down in the
>> new fw_cfg file. Does it?

> Yes.

Great, thanks.

>>> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
>>> index db32fd1..8fae3b9 100644
>>> --- a/hw/i386/acpi-build.c
>>> +++ b/hw/i386/acpi-build.c
>>> @@ -944,9 +944,8 @@ build_ssdt(GArray *table_data, GArray *linker,
>>>
>>>               scope = aml_scope("\\_SB");
>>>               dev = aml_device("PC%.02X", bus_num);
>>> -            aml_append(dev,
>>> -                       aml_name_decl("_UID", aml_string("PC%.02X",
>>> bus_num)));
>>> -            aml_append(dev, aml_name_decl("_HID",
>>> aml_string("PNP0A03")));
>>> +            aml_append(dev, aml_name_decl("_UID", aml_int(bus_num)));
>>> +            aml_append(dev, aml_name_decl("_HID",
>>> aml_eisaid("PNP0A03")));
>>>               aml_append(dev, aml_name_decl("_BBN", aml_int(bus_num)));
>>>
>>>               if (numa_node != NUMA_NODE_UNASSIGNED) {
>>
>> As far as I can see in the QEMU source, filling in _HID and _UID like
>> this is existing practice.

> I can submit the patch , (or you can submit and I'll ack) on top of PXB
> series.

I think I'll apply this locally for now, and test it together with the
OVMF code I plan to write. One of us can submit it later (I'm unaware of
any urgency, but I might be wrong).

> I am going to be on PTO, so it will wait a week :)

Works for me. Have a nice vacation. :)

Thanks!
Laszlo