Re: /proc/pci deprecation?

From: Adam J. Richter (
Date: Mon Dec 09 2002 - 04:15:24 EST

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.

Adam J. Richter __ ______________ 575 Oroville Road \ / Milpitas, California 95035
+1 408 309-6081 | g g d r a s i l United States of America
                         "Free Software For The Rest Of Us."
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