Re: [linux-fbdev] Retrace

On Tue, 8 Feb 2000, Benjamin Herrenschmidt wrote:

On Tue, Feb 8, 2000, Gabriel Paubert [off-list ref] wrote:

quoted

On x86 you have /dev/port which is disabled on PPC. I once or twice
suggested (but was greeted with a deafening silence) that we could
resurrect it and add an mmap method so that privileged programs may access
I/O ports with:

io_fd= open("/dev/port", O_RDWR);
iobase=mmap(0, device_size, PROT_READ|PROT_WRITE, MAP_SHARED,
		io_fd, device_base);

quoted

Unfortunately, with weird host bridges like Apple Uni-N (that has 3
busses with 3 different io bases but the same bus number), it's almost
impossible to get it correct, or eventually by parsing /proc/device-tree.

Not a problem if device_base is unique, you have to check that
device_base+device_size fits within one area. It must be unique at one
point to distinguish them from the processor perspective.

device_base may not be unique. Actually, that depends what is device_base
and how it's retreived. But for example, reading the BARs can give you
identical io base for devices on different sub-bridges, the distinction
beeing done by the iobase of the bridge itself.

The BAR values in PCI config space may be the same, but the BAR values in
struct pci_dev can be made different by the machine-specific fixup code.

Gr{oetje,eeting}s,
--
Geert Uytterhoeven -- Linux/{m68k~Amiga,PPC~CHRP} -- 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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