Re: kernel mapping

[Ralph Blach <rcblach@raleigh.ibm.com>]

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Why do we need simulated bat registers.

Chip

Frank Rowand wrote:
>
> Dan Malek wrote:
> >
> > How come we don't use iopa() and friends for all kernel mapping
> > information?  It is only defined for CONFIG_APUS, but is the right
> > thing to use on 8xx and 4xx, and probably all processors.  The
> > virt_to_bus/bus_to_virt contain the quickie arithmetic hack with
> > KERNELBASE, but that isn't the right thing to do for any kmalloc()
> > or valloc() space or if you don't have BAT mapping.
> >
> > I am considering making these functions more generic, removing the
> > #ifdefs, and implementing "simulated" BAT mapping for processors
> > like the 8xx and 4xx that don't have BATs (not for 2.4, of course :-).
> >
> > Why shouldn't I do this?
> >
> >         -- Dan
>
> For the 405 I had to use iopa() for virt_to_bus() because there are
> cases where I create a virtual address for IO buffers that is
> uncached, and that virtual address is not (physical address + KERNELBASE).
> I also have the beginnings of simulated BAT mapping for the 405
> (not quite there, but part way).
>
> -Frank
> --
> Frank Rowand <frank_rowand@mvista.com>
> MontaVista Software, Inc
>

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