mlx4 fails ("go bit not cleared") without MSI

[Bjorn Helgaas]

Hi Eugenia,

Due to my own stupidity, I tried to use mlx4 without turning on
CONFIG_PCI_MSI=y.  The driver failed miserably:

  pci 0000:01:00.0: [15b3:1007] type 00 class 0x020000
  mlx4_core: Mellanox ConnectX core driver v2.2-1 (Feb, 2014)
  mlx4_core: Initializing 0000:01:00.0
  mlx4_core 0000:01:00.0: PCIe link speed is 8.0GT/s, device supports 8.0GT/s
  mlx4_core 0000:01:00.0: PCIe link width is x8, device supports x8
  mlx4_core 0000:01:00.0: command 0x23 timed out (go bit not cleared)
  mlx4_core 0000:01:00.0: device is going to be reset
  mlx4_core 0000:01:00.0: device was reset successfully
  mlx4_core 0000:01:00.0: Failed to initialize queue pair table, aborting
  mlx4_core: probe of 0000:01:00.0 failed with error -5

The lack of MSI was my own fault, but it took me a long time to figure it
out.

The fact that mlx4 has a "msi_x" module parameter makes me think that
mlx4 is *supposed* to work without MSI.  Would you consider either
fixing the non-MSI fallback path, or printing a warning when the
driver can't set up MSIs?

This is easy to reproduce; just turn off CONFIG_PCI_MSI or boot with
"pci=nomsi".

Bjorn