On Mon, 2023-02-20 at 13:53 +0100, Niklas Schnelle wrote:
> On Fri, 2023-02-17 at 17:15 -0600, Bjorn Helgaas wrote:
> > On Tue, Feb 14, 2023 at 10:49:10AM +0100, Niklas Schnelle wrote:
> >
> >
---8<---
> > Other random questions unrelated to this patch:
> >
> > - zpci_bus_create_pci_bus() calls pci_bus_add_devices(). Isn't that
> > pointless? AFAICT, the bus->devices list is empty then.
>
> Yes I think you're right it does nothing and can be dropped.
>
> >
> > - What about zpci_bus_scan_device()? Why does it call both
> > pci_bus_add_device() and pci_bus_add_devices()? The latter will
> > just call the former, so it looks redundant. And the latter is
> > locked but not the former?
>
> Hmm. great find. This seems to have been weird and redundant since I
> first used that pattern in 3047766bc6ec ("s390/pci: fix enabling a
> reserved PCI function"). I think maybe then the reason for this was
> that prior to 960ac3626487 ("s390/pci: allow zPCI zbus without a
> function zero") when the newly enabled is devfn == 0 there could be
> functions from the same bus which would not have been added yet. I'm
> not sure though. That was definitely the idea behind the
> zpci_bus_scan_bus() in zpci_scan_configured_devices() that is also
> redundant now as we can now scan each function as it appears.
>
> This will definitely need to be cleaned up.
>
I'm working on cleaning this up but I'm a little confused by what
exactly needs to be under the pci_rescan_remove lock. For example the
pci_bus_add_device(virtfn) at the end of pci_iov_add_virtfn() doesn't
seem to be under the lock while most calls to pci_bus_add_devices()
are, most prominently the one in acpi_pci_root_add() which I assume is
what is used on most x86 systems. Any hints?
Also I think my original thought here might have been a premature worry
about PCI-to-PCI bridges thinking that adding the new device could lead
to more devices appearing. Of course actually thinking about it a bit
more there are quite a few other things that won't work without further
changes if we wanted to add bridges e.g. we would need to create
zpci_dev structs for these somewhere.
