[openib-general] Re: understanding mthca_alloc_db()

[Roland Dreier]

    > Where can I read about it? I have the documentation file:
    > InfiniHost_Programmers_Reference_Manual_1_16.pdf but see no
    > mention of this. Can you give any pointer to this info?

You need the InfiniHost III PRM -- the manual you have now is for
non-mem-free HCAs.

    > We would like to do rdma to memory mapped I/O so a remote node
    > can write, for example, directly to a device. We mapped some
    > virtual address to the physical address of the device. When we
    > tried to register this virtual memory area the ib driver failed
    > (get_user_pages() failed).  Can you please advice about how to
    > make this work?

It will be a little tricky to do this.  You need to register a memory
region that is mapped to the bus addresses of your MMIO region.  You
could create a new kernel interface to do this (hacky but not too
hard) or enhance get_user_pages() to handle MMIO regions (cleaner but
more difficult).

 - R.