Re: [PATCH v6 0/8] PCI: hv: Support host bridge probing on ARM64

[Boqun Feng]

On Thu, Aug 19, 2021 at 03:17:58PM +0100, Lorenzo Pieralisi wrote:
> On Tue, Jul 27, 2021 at 02:06:49AM +0800, Boqun Feng wrote:
> > Hi,
> > 
> > This is the v6 for the preparation of virtual PCI support on Hyper-V
> > ARM64, Previous versions:
> > 
> > v1:	https://lore.kernel.org/lkml/20210319161956.2838291-1-boqun.feng@xxxxxxxxx/
> > v2:	https://lore.kernel.org/lkml/20210503144635.2297386-1-boqun.feng@xxxxxxxxx/
> > v3:	https://lore.kernel.org/lkml/20210609163211.3467449-1-boqun.feng@xxxxxxxxx/
> > v4:	https://lore.kernel.org/lkml/20210714102737.198432-1-boqun.feng@xxxxxxxxx/
> > v5:	https://lore.kernel.org/lkml/20210720134429.511541-1-boqun.feng@xxxxxxxxx/
> > 
> > Changes since last version:
> > 
> > *	Rebase to 5.14-rc3
> > 
> > *	Comment fixes as suggested by Bjorn.
> > 
> > The basic problem we need to resolve is that ARM64 is an arch with
> > PCI_DOMAINS_GENERIC=y, so the bus sysdata is pci_config_window. However,
> > Hyper-V PCI provides a paravirtualized PCI interface, so there is no
> > actual pci_config_window for a PCI host bridge, so no information can be
> > retrieve from the pci_config_window of a Hyper-V virtual PCI bus. Also
> > there is no corresponding ACPI device for the Hyper-V PCI root bridge,
> > which introduces a special case when trying to find the ACPI device from
> > the sysdata (see patch #3).
> > 
> > With this patchset, we could enable the virtual PCI on Hyper-V ARM64
> > guest with other code under development.
> > 
> > Comments and suggestions are welcome.
> > 
> > Regards,
> > Boqun
> > 
> > Arnd Bergmann (1):
> >   PCI: hv: Generify PCI probing
> > 
> > Boqun Feng (7):
> >   PCI: Introduce domain_nr in pci_host_bridge
> >   PCI: Support populating MSI domains of root buses via bridges
> >   arm64: PCI: Restructure pcibios_root_bridge_prepare()
> >   arm64: PCI: Support root bridge preparation for Hyper-V
> >   PCI: hv: Set ->domain_nr of pci_host_bridge at probing time
> >   PCI: hv: Set up MSI domain at bridge probing time
> >   PCI: hv: Turn on the host bridge probing on ARM64
> > 
> >  arch/arm64/kernel/pci.c             | 29 +++++++---
> >  drivers/pci/controller/pci-hyperv.c | 86 +++++++++++++++++------------
> >  drivers/pci/probe.c                 | 12 +++-
> >  include/linux/pci.h                 | 11 ++++
> >  4 files changed, 93 insertions(+), 45 deletions(-)
> 
> If we take this series via the PCI tree we'd need Catalin/Will ACKs on
> patches 3-4.
> 

Got it.

> I need some time to look into [1] (thanks for that).
> 
> Without [1] patch 8 is ugly, that's no news. The question is whether
> it is worth waiting for a kernel cycle to integrate [1] into this series
> or not.
> 
> Is it really a problem if we postpone this series for another kernel
> cycle so that we can look into it ?
> 

Well, it's definitely better for me that we can have it in 5.15-rc1 ;-),
because it's a dependency for Hyper-V virtual PCI support on ARM64 and
we plan to send the rest of work in 5.15 cycle. And I can just base on
hyperv-next for the rest of the work if this is in 5.15-rc1. But yes,
it's not really a problem, since this one still needs to work with other
patches to support virtual PCI on ARM64 Hyper-V.

In fact, I personally don't think [1] is better than patch 8 (plus patch
3 & 4): playing with ->private seems dangerous and not very helpful on
readiblity, but I agree that we should explore every potential solution,
and that's why I send [1].

Regards,
Boqun

> [1] https://lore.kernel.org/lkml/20210811153619.88922-1-boqun.feng@xxxxxxxxx/