On Tue, 7 Mar 2006, Bjorn Helgaas wrote:
> On Tuesday 07 March 2006 07:21, linux-os (Dick Johnson) wrote:
>> Thinking that a device powers ON in a stable state is naive. Many
>> complex devices will have FPGA devices with floating pins that don't
>> become stable until their contents are loaded serially. Others will
>> have IRQ requests based upon power-on states that need to be cleared
>> with a software reset. One can't issue a software reset until the
>> device is enabled and enabling the device may generate interrupts
>> with no handler in place so you have a "can't get there from here"
>> problem.
>
> Maybe you could handle this with a PCI quirk that runs before
> pci_enable_device(). IIRC, we considered exposing a separate
> interface for PCI IRQ allocation and routing, but decided it
> wasn't worth the complexity since so few devices would need it.
>
The problem is that I can't write device internal registers to
put the device into a stable state without enabling the device.
So, the "fix" (read hack) was to mask off all possible interrupts
in the ioapic, call pci_enable_device(), initialize the device,
clear any pending hardware interrupts on the device, then reenable
the ioapic interrupts. I couldn't just use a spin-lock because
somebody complains and the machine panics.
>> Linux-2.4.x had IRQs that were stable. One could put
>> a handler in place that would handle the possible burst of interrupts
>> upon startup. Then this was changed so the IRQ value is wrong
>> until an unrelated and illogical event occurs.
>
> There are good reasons to wait to allocate the IRQ until you have
> a driver that cares about the device. I'm sorry that this broke
> your specific case.
>
> Bjorn
There are now other "standard" boards that seem to be experiencing
the same problem. Maybe it is time to make a procedure that turns
off interrupts for a specific device (not an unknown IRQ). Then
a subsequent call turns them on after the handler is in place.
This wouldn't affect current drivers. They would still turn on
hot by default.
Cheers,
Dick Johnson
Penguin : Linux version 2.6.15.4 on an i686 machine (5589.50 BogoMips).
Warning : 98.36% of all statistics are fiction, book release in April.
_
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