[ewg] Mellanox target workaround in SRP

[Vu Pham]

David Dillow wrote:
> On Mon, 2011-01-10 at 11:58 -0800, Vu Pham wrote:
>> David Dillow wrote:
>> > either. The SRP FMR mapping code is careful to mask the SG address with
>> > the FMR page mask, so we should never ask the HCA to map a page with the
>> > first_byte_offset != 0. Instead, we tell the target to request an IO
>> > virtual address appropriately offset into the first page of the FMR.
>> >
>> > Or perhaps I misunderstood you, and it's the non-zero first byte offset
>> > in the RDMA command on the wire that is the issue, and not the FMR setup
>> > in the initiator? And it only affects FMR-mapped memory, not the
>> > kernel's MR?
>>
>> It's not the kernel's MR.
>>
>> I suspect that the corruption happen with *only* Mellanox FMR + MPT
>> setup without fbo and target doing RDMA with offset vaddr.
>>
>> I need to ask internal hw/fw guys and confirm if it's true.
> 
> Have you had any response from the HW/FW guys?
> 

Sorry for late response.

Our hw/fw guys confirm that there is no problem, my suspect is wrong.

To explain clearly how hw translate from remote rdma address to physical address in fmr's MTT

X = requested/rdma_va - MPT.start + MPT.fbo
MTT index = X / MPT.blocksize
MTT offset = X % MPT.blocksize
PA = MTT[index] + MTT offset

MPT - memory protection table
MTT - memory translation table

-vu