[bugzilla-daemon@kernel.org: [Bug 216449] New: vfio-pci calls pci_bus_reset whenever a pci_release is triggered and refcnt is zero]

[bugzilla-daemon@kernel.org: [Bug 216449] New: vfio-pci calls pci_bus_reset whenever a pci_release is triggered and refcnt is zero]

[Bjorn Helgaas]

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https://bugzilla.kernel.org/show_bug.cgi?id=216449

I'm using vfio-pci to map an FPGA. I have an utility program that gets a file
descriptor for the device and does an mmap to read and write registers.

When I close the utility the FPGA is reset and all registers are gone. 
I wonder if this is the correct behaviour, I understand that the
vfio_pci_try_bus_reset is performed only when refcnt reaches zero but, in case
of other drivers, like UIO the behaviour is different. 

I expected to be able to close my utility and restart it and find the FPGA
registers at the last configured value.

The vfio_pci_try_bus_reset is in vfio_pci_disable that is called by
pci_release.

Probably even a module parameter to prevent calling vfio_pci_try_bus_reset
could be useful.