[Nouveau] How to check for proper MSI support?

[Yijing Wang]

>>> There is a NVIDIA G96 GPU (which is PCIe only) hanging off of a PCIe
>>> <-> PCI bridge (all on one card), which is plugged into a motherboard
>>> with the 430FX chipset (PCI 2.0 supported).
>>>
>>> The GPU PCI device, of course, has full support for MSI. However my
>>> understanding is that MSI won't actually work here. This is confirmed
>>> by the fact that if we let nouveau enable MSI, the device doesn't work
>>> (presumably due to lack of interrupt delivery, although I admit to not
>>> having debugged it that far). How do I, as a nouveau driver developer,
>>> know not to call pci_enable_msi? Or alternatively how can
>>> pci_enable_msi be taught not to succeed in this case?
>>
>> You can set bus_flags or global pci_msi_enable flag by add quirk function.
>> You can refer to examples in drivers/pci/quirk.c
>>
>> Linux support some broken chipsets or devices to disable msi during device initialization by add quirk.
> 
> So let me get this straight -- you're suggesting I add a quirk for
> every PCI chipset that doesn't support MSI? There are probably
> hundreds of these... anything made before 1999 or so, and probably a
> bunch since then too. There _has_ to be a way to do this generically.
> Is the PCI spec version anywhere in the root hub?

There is no register to identify PCI spec version in PCI config space registers.
If your platform boot up with ACPI, you can setting ACPI FADT boot flag to disable MSI,
you can refer to this in ACPI 5.2.9.3 chapter "Fixed ACPI Description Table Boot Architecture Flags"


> 
> Perhaps we can check if every bridge on the way to the CPU has the MSI
> capability (including the root hub)? (And naturally _that_ won't
> work... on my sandybridge laptop, the host bridge doesn't have the MSI
> cap but the system most definitely supports MSI.)
> 
> Adding Bjorn... perhaps you know? Some of the info has been stripped
> out by now, you can see the full lspci -vvvxxx at
> http://marc.info/?l=linux-pci&m=140443441730503&w=2
> 
>   -ilia
> 
> .
> 


-- 
Thanks!
Yijing