On 7 Mar 2005, Eric W. Biederman wrote: > Alan Stern <[EMAIL PROTECTED]> writes: > > > Shared IRQs will always be a problem. And the PCI subsystem doesn't > > implement shutdown() methods; that seems like a pretty big hole. I guess > > individual drivers can always create their own, however. > > Not having seen this in practice what is the bad effect > that happens with shared irqs. I know there is a warning messages > but is there anything beyond this, such as the irq being stuck on?
The problem comes when two devices share an IRQ line and at least one of them is actively generating interrupt requests. An ethernet interface or a USB controller would make a good example, if they weren't shut down properly during a kexec reboot. Let's say devices A and B share the same IRQ, and B has an interrupt request pending. Initially all the IRQ lines are disabled; they only get enabled as drivers request them. So consider what happens when the driver for A is initialized. It will probe A and will request the IRQ line be enabled. B's outstanding request will immediately interrupt the processor. But since there's no driver loaded for B, nobody will claim the interrupt or clear its source. Result: The kernel warns about interrupts not owned by a driver, and automatically disables the IRQ line. Now device A is in trouble. Obviously it can't function correctly without interrupts. B will be in trouble too, when its driver loads. This is exactly what happened to Laurent Riffard in http://bugme.osdl.org/show_bug.cgi?id=4294 Read his full dmesg attachment; you can see where IRQ 5 was triggered as soon as one of the USB controllers enabled it. Apparently the other USB controller had a pending interrupt. Things wouldn't be quite so bad if setup_irq() would re-enable a disabled shared IRQ when another driver requests it, but it doesn't. Is this behavior a bug or is it deliberate? Alan Stern ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
