[openib-general] Re: [PATCH 5 of 13] ipath - use proper address translation routine

[Christoph Hellwig]

On Mon, May 01, 2006 at 12:00:00PM -0700, Roland Dreier wrote:
>     Arjan> do you really NEED the vaddr?  (most of the time linux
>     Arjan> drivers don't need it, while other OSes do) If you really
>     Arjan> need it you should grab it at dma_map time ...  (and
>     Arjan> realize that it's not kernel addressable per se ;)
> 
> Yes, they need some kind of vaddr.
> 
> It's kind of a layering problem.  The IB stack assumes that IB devices
> have a DMA engine that deals with bus addresses.  But the ipath driver
> has to simulate this by using a memcpy on the CPU to move data to the
> PCI device.
> 
> I really don't know what the right solution is.  Maybe having some way
> to override the dma mapping operations so that the ipath driver can
> keep the info it needs?

Or stop doing the dma mapping in the IB upper level drivers.  I told you
that we'll get broken hardware that doesn't want dma mapping in the upper
level driver, and pathscale created exactly that :)