[openib-general] Question on get_dma_mr()

[Devesh Sharma]

Thanks to all  of you


On 3/27/06, Roland Dreier <rdreier at cisco.com> wrote:
>
>     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


S/G entry ?

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.


What is the size of this region ? is there any limitation in providing this
size?

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.


Finally  you mean to say  in the implementation  of this function  providing
a unique L_Key and R_Key is sufficient. Is it?

- R.
>
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