On Sat, 20 Mar 2021 13:03:13 +0000, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Sat, Mar 20, 2021 at 1:54 PM Marc Zyngier <maz@xxxxxxxxxx> wrote: > > On Fri, 19 Mar 2021 21:12:46 +0000, > > > > > > > Ugh. pci_root_bus_fwnode() is another callback to find the > > > irq_domain. Only one call, from pci_host_bridge_msi_domain(), which > > > itself is only called from pci_set_bus_msi_domain(). This feels like > > > another case where we could simplify things by having the host bridge > > > driver figure out the irq_domain explicitly when it creates the > > > pci_host_bridge. It seems like that's where we have the most > > > information about how to find the irq_domain. > > > > Urgh. This is a perfect copy paste of the x86 horror, warts and all. > > I can't say I'm thrilled (another way to say "Gawd, Noes! Never!"). > > > > One thing I am sure of is that I do not want to add more custom > > indirection to build the MSI topology. We barely got rid of the > > msi_controller structure, and this is the same thing by another > > name. Probably worse, actually. > > > > In this case, I don't see the point in going via a fwnode indirection > > given that there is no firmware tables the first place. > > > > As for finding the irq domain from the host bridge, that's not doable > > in most cases on arm64, as it is pretty likely that the host bridge > > knows nothing about MSIs when they are implemented in the GIC (see my > > recent msi_controller removal series that has a few patches about > > that). > > > > Having an optional callback to host bridges to obtain the MSI domain > > may be possible in some cases though (there might be a chicken/egg > > problem for some drivers though...). > > I would expect that the host bridge driver can find the MSI domain > at probe time and just add a pointer into the pci_host_bridge > structure. In most cases, it doesn't implement it itself, and I'd be reluctant to duplicate information that can already be retrieved from somewhere else in a generic way (i.e. no PCI specific). M. -- Without deviation from the norm, progress is not possible.
