RE: [PATCH 06/16] ntb: add check and comment for link up to mw_count and mw_get_align

[Allen Hubbe]

Let me try that again...

From: Hubbe, Allen
> From: Logan Gunthorpe
> > On 6/29/2017 2:13 PM, Allen Hubbe wrote:
> > > Unfortunately, it is to work around hardware errata.  That is not so trivial to fix.
> >
> > Can you describe more what the work around is doing? Can you share the
> > code? It seems odd that a workaround is based on the alignment
> > restrictions of the mws.
> 
> Sure, while not making any claim that this is ready for upstream.
> 
> It is not a workaround for alignment restrictions of the mws.  It is a restriction to avoid the use of
> doorbells and scratchpads.  Memory windows are used exclusively.
> 
> Read msi-x local <addr,data> and send that to the peer:

https://github.com/ntrdma/ntrdma/blob/master/drivers/ntc/ntc_ntb_msi.c#L583

> Transform peer's addr to the memory window region:

https://github.com/ntrdma/ntrdma/blob/master/drivers/ntc/ntc_ntb_msi.c#L603

> Append a dma immediate value operation after other operations, to write the data at addr:

https://github.com/ntrdma/ntrdma/blob/master/drivers/ntc/ntc_ntb_msi.c#L1195

> 
> Above describes the workaround.
> 
> Used in the context of a rdma-over-ntb driver here:
> https://github.com/ntrdma/ntrdma/blob/master/drivers/infiniband/hw/ntrdma/ntrdma_qp.c#L1585
> 
> >
> > Logan