The initial implementation of PCI/MSI interrupt domains in the hierarchical
interrupt domain model used a shortcut by providing a global PCI/MSI
domain.

This works because the PCI/MSI[X] hardware is standardized and uniform, but
it violates the basic design principle of hierarchical interrupt domains:
Each hardware block involved in the interrupt delivery chain should have a
separate interrupt domain.

For PCI/MSI[X], the interrupt controller is per PCI device and not a global
made-up entity.

Unsurprisingly, the shortcut turned out to have downsides as it does not
allow dynamic allocation of interrupt vectors after initialization and it
prevents supporting IMS on PCI. For further details, see:

https://lore.kernel.org/lkml/20221111120501.026511281@linutronix.de/

The solution is implementing per device MSI domains, this means the
entities which provide global PCI/MSI domain so far have to implement MSI
parent domain functionality instead.

This series:

  - Fixup a dependency problem with CONFIG_GENERIC_MSI_IRQ

  - converts the x86 hyperv driver to implement MSI parent domain.

Changes in v2:

  - Add the first fixup patch to resolve a build failure

  - Add clarification to the TODO note.

 arch/x86/hyperv/irqdomain.c | 111 ++++++++++++++++++++++++------------
 drivers/hv/Kconfig          |   1 +
 drivers/irqchip/Kconfig     |   1 +
 3 files changed, 78 insertions(+), 35 deletions(-)

-- 
2.39.5