[openib-general] [PATCH] IB/documentation - add new file to Documentation/infiniband

[Ralph Campbell]

On Fri, 2006-11-10 at 14:58 -0500, James Lentini wrote:
> Replies below:
> 
> On Fri, 10 Nov 2006, Ralph Campbell wrote:
> 
> <snip>
> > > > +  Remote processes should use the same address for 'remote_addr'
> > > > +  as the local kernel's address as returned by the mapping functions
> > > > +  listed above.  The only difference is the local kernel uses the
> > > > +  'lkey' and the remote kernel uses the 'rkey'.
> > > 
> > > I found the above paragraph difficult to understand on the first 
> > > read. How about structuring the text similar to the user space 
> > > explanation above:
> > > 
> > >  The addresses returned by these mapping functions should be 
> > >  used for a struct ib_send_wr's 'remote_addr' field with the 
> > >  appropriate rkey.
> > 
> > OK.
> > I guess I was trying to point out that the address used with the
> > lkey or rkey will always be the same when accessing the same byte
> > of memory. It is just that the lkey is used when accessing memory
> > locally and the rkey is used to access the memory remotely.
> 
> That is a good way of looking at it.
> 
> <snip>
> > > > +  ib_reg_phys_mr()  This function returns a pointer to struct ib_mr.
> > > > +  It takes an array of device DMA addresses and lengths which are used
> > > > +  to describe the memory region.  These addresses are created by
> > > > +  calling the mapping functions listed for ib_get_dma_mr().
> > > 
> > > The iova is an in/out parameter. I recommend including a description 
> > > of how to initialize it:
> > > 
> > >  The 'iova' argument can be used by the caller to request an address 
> > >  to associate with the first byte of the address region. Upon return, 
> > >  the 'iova' argument is the ... <continue with below>
> > 
> > Iova was at one point in time an in/out parameter but was changed
> > to be just an in parameter some time ago.
> 
> At what point was this changed?

Maybe a year ago. I tried to find it in the SVN log but
didn't find which revision changed it.

> In the 1.2 IBTA spec, it is described as an in/out.
> 
> For mthca, the iova value is an input (see mthca_reg_phys_mr). 

The IBTA spec. wasn't changed.
The open-fabrics code was changed since none of the HCAs
returned a modified iova value.  Also, there are
currently no callers of ib_reg_phys_mr() that I know of.