linux-kernel - [PATCH v5 0/2] genirq: s390/pci: Migrate MSI interrupts to irqdomain API

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Message-Id: <20251121-implement-msi-domain-v5-0-d7e717dfd3f7@linux.ibm.com>
Date: Fri, 21 Nov 2025 06:32:17 +0100
From: Tobias Schumacher <ts@...ux.ibm.com>
To: Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>, Halil Pasic <pasic@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Tobias Schumacher <ts@...ux.ibm.com>, Farhan Ali <alifm@...ux.ibm.com>
Subject: [PATCH v5 0/2] genirq: s390/pci: Migrate MSI interrupts to
 irqdomain API

This patch series reworks the PCIe interrupt handling on s390 by
migrating it to use a proper MSI parent domain. Introducing a dedicated
MSI domain hierarchy aligns s390 PCIe support with the generic Linux IRQ
domain model. Currently s390 is one of the last architectures still using
the legacy API.

The migration splits the existing code in the legacy functions
arch_setup_msi_irqs() and arch_teardown_msi_irqs() into different
callbacks of the newly created MSI parent domain:

- zpci_msi_prepare(): prepare the allocation of per-device MSI IRQs.
      will be called once for each device before allocating individual
      IRQs and sets up for example the adapter aisb and aibv.
- zpci_msi_teardown(): reverts the effects of zpci_msi_prepare() and is
      called after all MSI IRQs are freed.
- zpci_msi_domain_alloc(): the allocation function for interrupts
- zpci_msi_domain_free(): revert the effects of zpci_msi_domain_alloc()
- zpci_compose_msi_msg(): create the MSI message to be written into the
      corresponding PCI config space.

* Patch 1 fixes an inconsistency in the irqdomain API. Internally, hw
  irqs are represented by an unsigned long int (irq_hw_number_t) while
  the external API in some cases takes an unsigned int as parameter.
  This fix was required in V2 of the patchset. Due to conceptual changes
  in patch 2 it is not required anymore for s390, but still seems
  sensible.
* Patch 2 implements IRQ domains for s390 PCI

Since patch 1 changes common APIs, some build tests were done for x86_64
and arm64. 

Signed-off-by: Tobias Schumacher <ts@...ux.ibm.com>
---
Changes in v5:
- removed two lines of superfluous code
- Link to v4: https://lore.kernel.org/r/20251120-implement-msi-domain-v4-0-a01be58e158a@linux.ibm.com

Changes in v4:
- remove flag MSI_FLAG_PCI_MSI_MASK_PARENT and mask/unmask callbacks
- use goto statements in zpci_bus_create_pci_bus()
- Link to v3: https://lore.kernel.org/r/20251118-implement-msi-domain-v3-0-6fe8feb2a93f@linux.ibm.com

Changes in v3:
- implement one MSI parent domain per PCI domain to further align the
  implementation with other architectures.
- Link to v2: https://lore.kernel.org/r/20251117-implement-msi-domain-v2-0-a110ea0721fe@linux.ibm.com

Changes in v2:
- fix directed interrupt setup and handling
- add flag MSI_FLAG_NO_AFFINITY in case of floating interrupts
- style adjustments according to review comments
- Link to v1: https://lore.kernel.org/r/20251112-implement-msi-domain-v1-0-103dd123de14@linux.ibm.com

---
Tobias Schumacher (2):
      genirq: Change hwirq parameter to irq_hw_number_t
      s390/pci: Migrate s390 IRQ logic to IRQ domain API

 arch/s390/Kconfig           |   1 +
 arch/s390/include/asm/pci.h |   4 +
 arch/s390/pci/pci_bus.c     |  21 ++-
 arch/s390/pci/pci_irq.c     | 333 +++++++++++++++++++++++++++-----------------
 include/linux/irqdesc.h     |   6 +-
 kernel/irq/irqdesc.c        |   6 +-
 6 files changed, 233 insertions(+), 138 deletions(-)
---
base-commit: 82ef9f0fac73cca3e7d776b095b5a7de1b0b88fc
change-id: 20251104-implement-msi-domain-dc1ea014580e

Best regards,
-- 
Tobias Schumacher <ts@...ux.ibm.com>