__ioremap_at() in 2.4.0-test9-pre2

[Paul Mackerras]

Matt Porter writes:

> Ick...agree here.  Of course, the serial driver could be changed to
> do other than inb/outb's for other archs and be passed the memory
> mapped address of the ports.

And the parallel port driver, and the floppy driver, and the
keyboard/mouse drivers, and the ...

> This looks to be a good solution if we can't resolve to make the kernel
> less legacy-oriented.  I changed the default K2 board memory map to

If we only supported powermacs, and not preps or chrps, then we
probably could make the kernel less "legacy-oriented". :-) :-)

> do a similar thing by orienting the 2nd host bridge right after the
> 1st in the physical map.  The virt->phys mapping was then 1:1 and things
> work as you describe above.  Obviously, this approach won't work when
> you have separate bridge ASICs since you can't get the memory map
> granularity that I had in the dual host bridge package.

So we set up the virtual -> physical mapping to suit ourselves.  Not a
problem.

> Well, on drivers like the de4x5 you switch to use the mem bar instead
> of the I/O bar and then it's generic.  There are lots of drivers that
> given the choice, chose to use I/O calls.  These can easily be fixed.

But what is wrong with using registers in I/O space and accessing them
with in*/out*?  I don't understand the aversion some people have shown
to using in*/out*.  They are the accessor functions for PCI I/O space,
that's all.  Whatever happens, we need accessor functions for PCI I/O
space.  We can call them something different or make them more
complicated but that would just create extra work for ourselves and
make it harder to port drivers between architectures.

> PCI I/O is memory mapped on everything but x86.  In most cases PCI

So???  What we have is a level of abstraction that hides (from driver
authors) exactly how PCI memory and I/O space are accessed.  We have
readb/writeb etc. for PCI memory space and inb/outb etc. for PCI I/O
space.  The fact that on PPC both are mapped into the processor's
address space and accessed using loads and stores is something that
drivers should not care in the slightest about.  And in fact these
spaces are not accessed this way on some other non-intel platforms;
e.g. sparc64 uses special ldasi/stasi instructions.

> devices provide bars that map the same set of registers into both
> I/O space and mem space.  That leaves only the true legacy devices
> which have no memory bars to be concerned with.  It's a smaller
> set of drivers that need different low level access methods than
> you're making it out to be.

The fact remains that a lot of drivers will continue to use inb/outb
etc., since they are developed primarily on the intel platform.  It
makes sense for us to have an inb/outb that works similarly to intel,
so that we can use as many drivers as possible with as little pain as
possible.

Paul.

--
Paul Mackerras, Senior Open Source Researcher, Linuxcare, Inc.
+61 2 6262 8990 tel, +61 2 6262 8991 fax
paulus at linuxcare.com.au, http://www.linuxcare.com.au/
Linuxcare.  Support for the revolution.

** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/