With the device in an HP, I can view the PCIe Link Capability register.
I find that it has a value of 843f483.
Ignoring the 'port #' field, I find that this indicates:
supported link speeds: 3 (no idea how to interpret)
max link width: 8
Active State PM support: <11:10> = 1
Data Link Layer Active Reporting Capable: <20> = 0
Link B/W Notification Capable: <21> = 0
Bit 22 Reserved: = 1
The EchoExpressPro Link Capability register is 333fc41
Bit 22 Reserved = 0
<21> = 1
<20> = 1
<11:10> = 3
Don't know if it enforces any of these to be certain values, in particular <11:10>.
I can find no clear description of the PCI config space settings in any of the Mellanox docs.
I am used to having an explicit (often wrong) enumeration of the PCI config space settings for a device.
If there some other manual I am missing?
The Mellanox card supports L0s, but not L1 ASPM.
This sounds like it might be the crux of the biscuit, but I note that the Intel 82599EB I have only supports L0s, and I was under the impression that at least some Intel 10Gig cards were certified as working: the SmallTree 82599-based product is on the supported list.