Interrupt sharing.

David Woodhouse (dwmw2@cam.ac.uk)
Wed, 12 Feb 1997 12:47:35 +0000

I have two network cards in my Linux box - a Realtek 8029 and a 3Com 3c509.
The former has support in the kernel, and the latter is available as a module.
If I tell them both to use the same interrupt, the first card will work fine
until I ifconfig the second, at which point it takes over the IRQ and never
gives it back. Is this the correct behaviour? Should they be able to share the
interrupts? If not, should not the 3c509 driver at least restore the IRQ
handler to it's original state when it finishes, so the other card can
continue working?

Also, the 3c509 driver attempts to release the IRQ twice - once when
ifconfig'ed down and again when the module is removed. Is this a hangover from
the time when it used to hog the IRQ all the time it was installed?

With regard to sharing of interrupts, will the kernel handle more than one
serial port on the same IRQ simultaneously (i.e. COM1/3, COM2/4) ?
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