[+cc Yinghai]
On Tue, Jul 15, 2014 at 9:34 PM, Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx> wrote:
> Hi Bjorn,
> When enabling ACPI based IOAPIC hotplug, we encountered an
> issue with PCI IRQ reference count tracking and need your advices.
> In order to hot-remove an IOAPIC, we need to track and keep
> balance of IOAPIC pin usage count. But acpi_pci_irq_enable() may
> be called twice for a PCI device,
> 1) pci_acpi_init() if pci_routeirq is true
> 2) pci_enable_device()
>
> So in function acpi_pci_irq_enable(), we need a way to track whether
> an IOAPIC IRQ has been assigned to the PCI device. Previously we check
> "if (dev->irq > 0)" for that, but that's wrong because dev->irq may
> be set to non-zero in pci_read_irq() if BIOS has already assigned
> a legacy IRQ for the device. So is it OK to add a flag into pci_dev
> to track this information?
>
> Another possible workaround is to disable IOAPIC hotplug when
> pci_routeirq is set, but that sounds not the best solution.
My first choice would be to get rid of pci_routeirq. It was added in
2004 as a workaround for broken drivers. I don't know any reason why
we need the "pci=routeirq" option any more.
However, 629e15d245f4 ("x86, irq: update_mptable needs pci_routeirq")
added another use of pci_routeirq. This is only used when booting
with the undocumented "update_mptable" option, and I can't tell
whether it's useful or not.
Bjorn
P.S. I'm going on vacation for a few weeks, so I won't be able to
follow this for a while.
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