[openib-general] Question on get_dma_mr()

[Roland Dreier]

    Devesh> Hello all, Please any body explain me about the
    Devesh> functionality of verbs ib_get_dma_mr()?

Actually, the responses you've gotten are not quite right.
ib_get_dma_mr() returns a memory region that can be used for any _bus_
addresses.  In other words, if an S/G entry is passed to the driver
that uses the L_Key from ib_get_dma_mr() and an address of, say,
0xdeadbeef, then the RDMA device should use a bus address of
0xdeadbeef to access that memory.

The difference between bus addresses and physical addresses is
significant when IOMMUs are present.

This is somewhat similar to the verbs extensions notion of "reserved
L_Key," except that it also provides an R_Key and the ability to
specify the access permissions of the region.

 - R.