[PATCH kernel] vfio_pci_nvlink2: Do not attempt NPU2 setup on old P8's NPU

[Michael Ellerman]

Alexey Kardashevskiy <aik at ozlabs.ru> writes:
> On 13/11/2020 16:30, Andrew Donnellan wrote:
>> On 13/11/20 4:06 pm, Alexey Kardashevskiy wrote:
>>> We execute certain NPU2 setup code (such as mapping an LPID to a device
>>> in NPU2) unconditionally if an Nvlink bridge is detected. However this
>>> cannot succeed on P8+ machines as the init helpers return an error other
>>> than ENODEV which means the device is there is and setup failed so
>>> vfio_pci_enable() fails and pass through is not possible.
>>>
>>> This changes the two NPU2 related init helpers to return -ENODEV if
>>> there is no "memory-region" device tree property as this is
>>> the distinction between NPU and NPU2.
>>>
>>> Fixes: 7f92891778df ("vfio_pci: Add NVIDIA GV100GL [Tesla V100 SXM2] 
>>> subdriver")
>>> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
>> 
>> Should this be Cc: stable?
>
> This depends on whether P8+ + NVLink was ever a  product (hi Leonardo) 
> and had actual customers who still rely on upstream kernels to work as 
> after many years only the last week I heard form some Redhat test 
> engineer that it does not work. May be cc: stable...

I don't think it really matters if it was a product or not. Upstream is
never a product anyway.

If the fix is simple and unlikely to introduce a regression, and would
potentially save someone having to debug the problem again, then it
should get backported to stable.

You should also clarify what you mean by "P8+", it won't be clear to
most readers if you mean "Power 8 and/or later" or specifically Naples /
Power8 NVL.

cheers