Re: __ioremap_at() in 2.4.0-test9-pre2

On Tue, 19 Sep 2000, Matt Porter wrote:

On Wed, Sep 20, 2000 at 09:58:07AM +1100, Paul Mackerras wrote:

quoted

Matt Porter writes:

quoted

On Tue, Sep 19, 2000 at 02:59:02PM +1100, Paul Mackerras wrote:

One solution that has been proposed is to set the base I/O port number
in the pci_dev structure to be actually the virtual address where you
can access that I/O port.  I don't like that solution because it means
that drivers for legacy PC-style devices can't do inb/outb to the
usual well-known port numbers and find the device they expect.  For
example, inb(0x3f8) won't access the first serial port (this is on
machines such as prep and some chrp which have a lot of PC-style
devices).

Another option would be to use a translation table. If you limit I/O space to
64 kB (like on PC), you waste only 256 kB of memory (assuming a table with
32-bit pointers). With a multi-level tree or a smarter pointer scheme, you can
limit the waste even more. Since I/O accesses are intrinsically slow, the
overhead is minimal.

I agree this solution is not optimal, though.

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.

These days serial.c does support MMIO on PCI devices. In fact it supports
everything that looks even remotely like a NS16550 (hence it should be renamed
16550.c), both in I/O and in memory space.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


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