Re: How does one get physical address for iorempped window?

virt_to_*/*_to_virt functions _should_ have become
something more generic, but they are just yet another macro
name for doing the same thing.  Now, we have gone of and
created some pci_* mapping functions, which are not at all
useful for highly integrated processors because their
integrated features are not PCI devices.  Yet another set
of functions for integrated processors?  I don't think so.

I think that requiring knowledge of the object attributes
for a VM or physical space so you can call the proper
mapping or other management functions is just a poor
design.  If you know this information and wish to take
performance enhancement shortcuts, that's fine, but it
shouldn't be required.

What if you're working on a system with multiple PCI
busses (or even multiple disparate bus types) and it's
not possible to map Host memory at the same address on
all busses?  Being able to refer to something like, say,
the appropriate pci_bus* when invoking virt_to_bus()
could make it possible to accomodate those different
mappings.  I'm certainly not a fan of pointlessly
complex code, but the one-size-fits-all implementation
of virt_to_bus() seen in my 25Jan-vintage kernel sources
(it just lops off the KERNEL_OFFSET bits and adds
pci_dram_offset) won't work in situations such as those
I just described.


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mod+linuxppc-embedded@world-f.std.com wrote:

.....  Being able to refer to something like, say,
the appropriate pci_bus* when invoking virt_to_bus()

Right, you have to provide enough information to get the
job done correctly, but this could be more generic.  Adding
pci_bus* to virt_to_bus is the right concept, but the wrong
implementation as I certainly want to use virt_to_bus() (or
whatever) for devices that are not on a PCI bus.

...  I'm certainly not a fan of pointlessly
complex code, but the one-size-fits-all implementation
of virt_to_bus()....

That's not a one-size-fits-all implementation :-).  It (and
virt_to_phys()) worked differently on at least three different
PowerPC implementations.  Mainly to eliminate a bunch of nested
#ifdefs and duplicated code, I now use the same implementation
on all PowerPCs, but it is just the first small step to doing
something better.


	-- Dan

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