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From"Adam J. Richter" <>
DateMon, 9 Dec 2002 01:15:24 -0800
SubjectRe: /proc/pci deprecation?
Digg This
Linus Torvalds wrote:
- we should _never_ update the PCI_INTERRUPT_LINE register, because it destroys boot loader information (the same way we need to not overwrite BIOS extended areas and ACPI areas etc in order to be able to reboot cleanly)

I don't think the kernel presently does this, but if it were to actually do the chipset-specific programming change the IRQ routing of a device, it should update PCI_INTERRUPT_LINE precisely so that the information will be passed on across a soft reboot.
This comes up for me because I have daone motherobard with a BIOS that never programs the USB controller's interrupt line, so I have to do the chipset-specific bit twiddling (which, in this case happens to be simply writing the desired irq into the device's PCI_INTERRUPT_LINE register anyhow). By the way, I also had to change arch/i386/kernel/pci.c to get it to reread PCI_INTERRUPT_LINE if it thought the interrupt was not routed, although all that I would really need is some way for a user level program to persuade the kernel to believe that a particular PCI device's interrupt line A has changed to irq n.

This exception is probably not relevant to what Linus and Richard are discussing, but I thought should mention it, lest that "_never_" be interpreted too absolutely.

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