Re: [PATCH v6 2/2] s390/pci: Migrate s390 IRQ logic to IRQ domain API

[Gerd Bayer <gbayer@linux.ibm.com>]

On Fri, 2025-11-21 at 16:45 +0100, 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 devfn and the MSI index.
> 
> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
> 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     |  18 ++-
>  arch/s390/pci/pci_irq.c     | 304 ++++++++++++++++++++++++++++----------------
>  4 files changed, 212 insertions(+), 115 deletions(-)
> 

LGTM now,
Reviewed-by: Gerd Bayer <gbayer@linux.ibm.com>

Thank you!