Re: [PATCH v4 2/2] s390/pci: Migrate s390 IRQ logic to IRQ domain API

[Farhan Ali <alifm@linux.ibm.com>]

On 11/20/2025 2:27 AM, Tobias Schumacher wrote:
> s390 is one of the last architectures using the legacy API for setup and
> teardown of PCI MSI IRQs. Migrate the s390 IRQ allocation and teardown
> to the MSI parent domain API. For details, see:
>
> https://lore.kernel.org/lkml/20221111120501.026511281@linutronix.de
>
> In detail, create an MSI parent domain for each PCI domain. When a PCI
> device sets up MSI or MSI-X IRQs, the library creates a per-device IRQ
> domain for this device, which is used by the device for allocating and
> freeing IRQs.
>
> The per-device domain delegates this allocation and freeing to the
> parent-domain. In the end, the corresponding callbacks of the parent
> domain are responsible for allocating and freeing the IRQs.
>
> The allocation is split into two parts:
> - zpci_msi_prepare() is called once for each device and allocates the
>    required resources. On s390, each PCI function has its own airq
>    vector and a summary bit, which must be configured once per function.
>    This is done in prepare().
> - zpci_msi_alloc() can be called multiple times for allocating one or
>    more MSI/MSI-X IRQs. This creates a mapping between the virtual IRQ
>    number in the kernel and the hardware IRQ number.
>
> Freeing is split into two counterparts:
> - zpci_msi_free() reverts the effects of zpci_msi_alloc() and
> - zpci_msi_teardown() reverts the effects of zpci_msi_prepare(). This is
>    called once when all IRQs are freed before a device is removed.
>
> Since the parent domain in the end allocates the IRQs, the hwirq
> encoding must be unambiguous for all IRQs of all devices. This is
> achieved by encoding the hwirq using the PCI function id and the MSI
> index.
>
> Signed-off-by: Tobias Schumacher<ts@linux.ibm.com>
> ---
>   arch/s390/Kconfig           |   1 +
>   arch/s390/include/asm/pci.h |   4 +
>   arch/s390/pci/pci_bus.c     |  21 ++-
>   arch/s390/pci/pci_irq.c     | 335 +++++++++++++++++++++++++++-----------------
>   4 files changed, 229 insertions(+), 132 deletions(-)

Thanks for making the changes!

Reviewed-by: Farhan Ali <alifm@linux.ibm.com>