[ewg] Mellanox target workaround in SRP

[Roland Dreier]

Maybe we can use MST's current email to ask him... Michael, do you have
any memory of the issue we worked around here?

 > I have question regarding workaround introduced in commit 559ce8f1 of
 > the mainline tree:
 > 
 >     IB/srp: Work around data corruption bug on Mellanox targets
 >     
 >     Data corruption has been seen with Mellanox SRP targets when FMRs
 >     create a memory region with I/O virtual address != 0.  Add a
 >     workaround that disables FMR merging for Mellanox targets (OUI 0002c9).
 > 
 > I don't see how this can make a difference to the target -- it sees an
 > address and length, and there should be no visible difference to it when
 > it gets an FMR versus a direct-mapped region of the same space, right?
 > And how is it different than getting a direct or indirect descriptor
 > with a similar offset?
 > 
 > I could see there being a bug on the initiator HCA not liking such FMR
 > mappings, but then it should be keyed off of the vendor of our HCA and
 > not the target.
 > 
 > I'm sure this was tested and shown to fix the problem; I'm just confused
 > as to what the problem really was and if this is still relevant. Can
 > someone please enlighten me?