On Wed, 18 Sep 1996 12:52:12 -0500 (CDT) 
 Scott Reynolds <scottr@Plexus.COM> wrote:

 > > Would someone please explain to me whether everyone shares the attitude
 > > that if it's not MI, it should not be implemented whatsoever? 
 > 
 > Not everyone shares this attitude.  I suspect very few people even have
 > it, but due to the limitations of the communications medium, I can see why
 > you would have that impression.

I certainly don't have this attitude.  I implement machine-dependent 
things all the time... I do, however, have a problem with making 
machine-dependent changes to files which are (or are supposed to be) 
machine-independent.

The problems with the bounce-buffer stuff that everyone is currently 
talking about are:

	- They are currently _very_ i386-specific.

	- They make it much harder to convert the drivers that need them
	  to a machine-independent DMA mapping system. [*]

[*] A machine-independent DMA mapping system really _is_ what is 
required; before each DMA transfer, the buffer will be mapped into 
DMA-able space (on the alpha, this means finding the physical page 
containing the buffer, and programming some DMA mapping registers and 
tranlating the host memory address to the memory range as seen by the ISA 
bus ... on the i386, it means allocating a bounce-buffer in memory that 
the ISA can see), the DMA controller on the card told which address to 
DMA too (returned by the DMA mapping function), the DMA will happen, and 
the buffer will be un-mapped (on the alpha, undoing the programming you 
did before, on the i386, bcopy()ing the bounce-buffer's contents to the 
buffer the caller provided).  (Yeesh!  What a long sentence! :-)

Anyhow, the point is that this is going to reqire some drivers to be 
restructured a bit ... restructuring them in the _opposite_ direction 
now would make that much harder to fix them later.

 -- save the ancient forests - http://www.bayarea.net/~thorpej/forest/ -- 
Jason R. Thorpe                                       thorpej@nas.nasa.gov
NASA Ames Research Center                               Home: 408.866.1912
NAS: M/S 258-6                                          Work: 415.604.0935
Moffett Field, CA 94035                                Pager: 415.428.6939