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<648e6fa0333882bd4b8503688306969cfeeeb249.camel@linux.ibm.com> Subject: Re: [PATCH v2 2/2] s390/pci: Migrate s390 IRQ logic to IRQ domain API From: Niklas Schnelle To: Tobias Schumacher , Farhan Ali Cc: Tobias Schumacher , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Gerald Schaefer , Gerd Bayer , Halil Pasic , Matthew Rosato , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Date: Tue, 18 Nov 2025 11:15:36 +0100 In-Reply-To: References: <20251117-implement-msi-domain-v2-0-a110ea0721fe@linux.ibm.com> <20251117-implement-msi-domain-v2-2-a110ea0721fe@linux.ibm.com> <933dea7a-4e5a-4d3c-8580-b94d0a9271c1@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; prefer-encrypt=mutual; keydata=mQINBGHm3M8BEAC+MIQkfoPIAKdjjk84OSQ8erd2OICj98+GdhMQpIjHXn/RJdCZLa58k /ay5x0xIHkWzx1JJOm4Lki7WEzRbYDexQEJP0xUia0U+4Yg7PJL4Dg/W4Ho28dRBROoJjgJSLSHwc 3/1pjpNlSaX/qg3ZM8+/EiSGc7uEPklLYu3gRGxcWV/944HdUyLcnjrZwCn2+gg9ncVJjsimS0ro/ 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12:59 AM, Tobias Schumacher wrote: > --- snip --- >=20 > > > diff --git a/arch/s390/pci/pci_bus.c b/arch/s390/pci/pci_bus.c > > > index=20 > > > be8c697fea0cc755cfdb4fb0a9e3b95183bec0dc..2be33cfb8970409db4fcb75ea73= 543f49b583a5c=20 > > > 100644 > > > --- a/arch/s390/pci/pci_bus.c > > > +++ b/arch/s390/pci/pci_bus.c > > > @@ -210,6 +210,7 @@ static int zpci_bus_create_pci_bus(struct zpci_bu= s=20 > > > *zbus, struct zpci_dev *fr, s > > > } > > > zbus->bus =3D bus; > > > + zpci_set_msi_parent_domain(zbus); > >=20 > > Why are we setting the zpci_set_msi_parent_domain per root device > > instead of per zpci device? >=20 > On other architectures the parent domain is set once for the root bus.= =20 > During bus scanning, pci_device_add() then sets the domain in the device= =20 > by calling pci_set_msi_domain(). By adding the parent domain to the root= =20 > busses, we are using the same mechanisms and are as close as possible to= =20 > other architectures. >=20 I didn't think about this enough, but reading your argument I wonder if that points to having a parent domain per PCI domain vs having a single global one like you have at the moment. And since we're limited to one struct zpci_bus per PCI domain in the current code with struct zpci_bus::bus being a root bus and the zpci_bus also carrying the domain number, I think that would more closely match the parent domain per PCI domain model. As for Farhan's comment as I understand it the common code still creates child MSI domains for the individual zpci devices. So both a global parent domain as in this version or a per zpci bus domain will work we just want to keep things as similar to non virtual PCI topologies as possible I think. Thanks, Niklas