Messages in this thread |  | | From | Paul Mackerras <> | Date | Fri, 23 Nov 2001 14:55:29 +1100 (EST) | Subject | Re: problem accessing /dev/port |
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Christopher Friesen writes:
> To begin, I'm running 2.2.17 with some patches. > > I'm attempting to have a userspace app read and write I/O ports on a powerpc > machine. The obvious method (iopl()) doesn't seem to be available (using glibc, > but sys/io.h doesn't exist). > > When I try and access /dev/port with a small utility that works fine on my PIII, > I get the error message "Device not configured". The file exists in /dev and > has the same permissions on both machines.
If you look in drivers/char/mem.c you will see an #if that eliminates the statement filp->f_op = &port_fops if CONFIG_PPC is defined. The reason for this is that accessing a non-existent I/O port on powermacs generates a machine check interrupt which, in 2.2.x kernels, causes a panic. The situation is better in 2.4 because we catch the machine check and arrange for inb/w/l to return ~0.
> Do I need to enable something in the kernel to support this? Where is this > configured?
Change the #if line to take out the defined(CONFIG_PPC) part.
The other way to access I/O from userspace is to mmap /dev/mem at the offset that corresponds to the physical address where your PCI host bridge maps PCI I/O space, e.g. you would use an offset of 0xfe000000 for an MPC106 (grackle) bridge. Once again the situation is better in 2.4 since you can mmap the /proc/bus/pci/bb/dd.f file corresponding to your pci device and access its memory and I/O regions that way.
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