Messages in this thread | | | From | John Garry <> | Subject | PCI/kernel msi code vs GIC ITS driver conflict? | Date | Tue, 3 Sep 2019 15:09:36 +0100 |
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Hi Marc, Bjorn, Thomas,
We've come across a conflict with the kernel/pci msi code and GIC ITS driver on our arm64 system, whereby we can't unbind and re-bind a PCI device driver under special conditions. I'll explain...
Our PCI device support 32 MSIs. The driver attempts to allocate msi vectors with min msi=17, max msi = 32, and affd.pre vectors = 16. For our test we make nr_cpus = 1 (just anything less than 16).
We find that the pci/kernel msi code gives us 17 vectors, but the GIC ITS code reserves 32 lpi maps in its_irq_domain_alloc(). The problem then occurs when unbinding the driver in its_irq_domain_free() call, where we only clear bits for 17 vectors. So if we unbind the driver and then attempt to bind again, it fails.
Where the fault lies, I can't say. Maybe the kernel msi code should always give power of 2 vectors - as I understand, the PCI spec mandates this. Or maybe the GIC ITS driver has a problem in the free path, as above. Or maybe the PCI driver should not be allowed to request !power of 2 min/max vectors.
Opinion?
Thanks in advance, John
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