linux-kernel - [PATCH 0/1] um: MSI parent domain conversion

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Message-Id: <cover.1750947651.git.namcao@linutronix.de>
Date: Thu, 26 Jun 2025 16:47:14 +0200
From: Nam Cao <namcao@...utronix.de>
To: Marc Zyngier <maz@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Weinberger <richard@....at>,
	Anton Ivanov <anton.ivanov@...bridgegreys.com>,
	Johannes Berg <johannes@...solutions.net>,
	linux-um@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: Nam Cao <namcao@...utronix.de>
Subject: [PATCH 0/1] um: MSI parent domain conversion

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 converts the um's driver to implement MSI parent domain.

 arch/um/drivers/Kconfig    |  1 +
 arch/um/drivers/virt-pci.c | 46 +++++++++++++++++++-------------------
 2 files changed, 24 insertions(+), 23 deletions(-)

-- 
2.39.5