[linux-fbdev] Retrace

Gabriel Paubert paubert at iram.es
Tue Feb 8 20:29:59 EST 2000

On Mon, 7 Feb 2000, Benjamin Herrenschmidt wrote:

> On Mon, Feb 7, 2000, Geert Uytterhoeven <geert at linux-m68k.org> wrote:
> >And now the bad news: the address you have to mmap() depends on the machine
> >type :-(
> We need to find a solution for that one day or another. The iobase is not
> only arch-dependant (PReP, PowerMac, CHRP...) but also machine dependant,
> since it depends on the host bridge type.

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);

> 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.


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