Re: How to create PCH to support those existing driver

Chen, Tiejun
2014-08-18T09:01:29Z

On 2014/8/18 16:21, Michael S. Tsirkin wrote:
> On Mon, Aug 18, 2014 at 11:06:29AM +0800, Chen, Tiejun wrote:
>> On 2014/8/17 18:32, Michael S. Tsirkin wrote:
>>> On Fri, Aug 15, 2014 at 09:58:40AM +0800, Chen, Tiejun wrote:
>>>> Michael and Paolo,
>>>
>>> Please re-post discussion on list. These off list ones are just
>>> wasting time since they invariably have to be repeated on list again.
>>
>> Okay, now just reissue this discussion to all related guys. And do you think
>> we need to discuss in public, qemu and xen mail list?
>
> Absolutely.

Now -CC qemu, xen and intel-gfx.

If I'm missing someone important please tell me as well.

>
>>>
>>>> After I created that new machine specific to IGD passthrough, xenigd, now I
>>>> will step next to register the PCH.
>>>>
>>>> IIRC, our complete solution should be as follows:
>>>>
>>>> #1 create a new machine based on piix, xenigd
>>>>
>>>> This is done with Michael help.
>>>>
>>>> #2 register ISA bridge
>>>>
>>>> 1> Its still fixed at 1f.0.
>>>> 2> ISA bridge's vendor_id/device_id should be emulated but then
>>>>
>>>> subsystem_vendor_id = PCI_VENDOR_ID_XEN;
>>>> subsystem_device_id = ISA Bridge's real device id
>>>>
>>>> This mean we need to change driver to walk with this way.
>>>> For example, in
>>>> case of Linux native driver,
>>>>
>>>> intel_detect_pch()
>>>> {
>>>> ...
>>>> if (pch->subsystem_vendor == PCI_VENDOR_ID_XEN)
>>>> id = pch->subsystem_device & INTEL_PCH_DEVICE_ID_MASK;
>>>>
>>>> Then driver can get that real device id by 'subsystem_device', right?
>>>>
>>>> This is fine now but how to support those existing drivers which are just
>>
>> Here correct one point, we don't need to care about supporting the legacy
>> driver since the legacy driver still should work qemu-traditional. So we
>> just make sure the existing driver with this subsystem_id way can support
>> those existing and legacy platform.
>>
>> Now this is clear to me.
>>
>>>> dependent on checking real vendor_id/device_id directly,
>>>>
>>>> if (pch->vendor == PCI_VENDOR_ID_INTEL) {
>>>> unsigned short id = pch->device & INTEL_PCH_DEVICE_ID_MASK
>>>>
>>>> Maybe I'm missing something, please hint me.
>>>>
>>>> Thanks
>>>> Tiejun
>>>
>>> The subsystem id was just one idea.
>>
>> But from that email thread, "RH / Intel Virtualization Engineering Meeting -
>> Minutes 7/10", I didn't see other idea we should prefer currently.
>>
>>> What was finally agreed for future drivers is that guests will get all
>>> information they need from the video card, this ID hack was needed only
>>> for very old legacy devices.
>>> http://article.gmane.org/gmane.comp.freedesktop.xorg.drivers.intel/42258
>>> So this is for newer guests, they will work without need
>>> for hacks, like any other device.
>>>
>>
>> Actually we had a meeting to discuss our future solution, but seems you were
>> on vacation at that moment :)
>>
>> In that meeting we had an agreement between us and some upstream guys.
>>
>> We will have such a PCI capability structure in this PCI device to represent
>> all information in the future. This make sens to Intel as well.
>>
>> Maybe Allen or Paolo known more details.
>>
>> But obviously this a long-term solution, so currently we will work with this
>> subsystem_id way temporarily. And this way is accepted by those guys in the
>> meeting.
>
>
> I don't see the point really. If you are modifying the driver,

Yes, we need to modify something in the driver.

> why not modify it to its final form.

What's your final form?

As I track that email thread, seems the follows is just a way you guys
achieve a better agreement.

"
> why not set the subsys vid to the RH/Quamranet/Virtio VID, so it's
> obvious for the use-match?

That's exactly the suggestion. Though upstream they might be using the
XenSource id since the patches were for Xen.

Paolo
"
Or I'm missing something?

Thanks
Tiejun

>
>>>
>>> For existing drivers: Vendor ID is intel anyway.
>>
>> Yes.
>>
>>> For device ID, override it through a property
>>> or something. But I think poking at the real host from
>>> qemu is a mistake though, host is not
>>> protected by iommu.
>>> Two possible suggestions were to reverse-detect
>>> id of the device from the card that is assigned,
>>
>> I guess you're saying pci_get_device(vendor/devices_ids), right?
>>
>>> or just make it a user property, and move the smarts
>>> to management.
>>
>> Sorry could you elaborate this way in detail?
>>
>> Thanks
>> Tiejun
>
>
> Will do but let's do it on the mailing list.
>