[RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge

[Mason]

On 19/04/2017 13:19, Mason wrote:

> My biggest problem is that tango_unmask() is never called.

FTR, the missing incantation was:
Explicitly calling tango_{mask/unmask/ack} from the corresponding msi_{mask/unmask/ack}

Marc, I have one nagging doubt, wrt splitting MSI line selection
and MSI enable.

tango_irq_domain_alloc : finds an available MSI 'j' to allocate
tango_irq_domain_free : release MSI 'j'
tango_unmask : enable MSI 'j'
tango_mask : disable MSI 'j'

Is the following scenario guaranteed to never happen?

tango_irq_domain_alloc // alloc 0
tango_irq_domain_free  // free 0
tango_irq_domain_alloc // alloc 0
tango_unmask // enable 0
tango_unmask // enable 0 = NOP
tango_mask   // disable 0

In this theoretical scenario, we would be left with a non-functional
MSI 0.

Regards.