[openib-general] Reserved L_Key API

[Roland Dreier]

    Tom> I think this is a good idea.  Even if Tavor is limited on big
    Tom> mem systems, this would be fine.  There are many devices that
    Tom> cannot DMA into high memory regions for various reasons.

Tavor wouldn't be limited since it can create arbitrarily large memory
regions with translation off.  I'm thinking of other devices -- for
example, I have no documentation on the Fujitsu HCA (and in fact I've
never even seen one) but from looking at the InfiniCon/Agilent driver
in svn, it seems that it is limited to memory regions with pages of
max size 4 MB.  In my scheme they would be limited to DMA from the low 4G.

On the other hand even there I can think of hacks to get around the
problem -- the only systems where this limitation really causes
problems would be Intel IA-32 and EMT64T systems with > 4 GB of RAM
(since Intel has no IOMMU).  And for those systems the assumption that
RAM starts at PCI address 0 is valid, so you could just register a
region from 0 up to 0xfffffffff (ie the low 64 GB) and be happy.

In any case -- I'll go ahead and code this up early next week.

 - R.