Re: [PATCH v6 2/7] xen/arm: add pci-domain for disabled devices

[Julien Grall <julien@xxxxxxx>]

Hi Oleksandr,

On 17/11/2021 06:56, Oleksandr Andrushchenko wrote:
> Hi, Julien!
>
> On 16.11.21 20:48, Julien Grall wrote:
> > Hi Oleksander,
> >
> > On 05/11/2021 06:33, Oleksandr Andrushchenko wrote:
> > > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > >
> > > If a PCI host bridge device is present in the device tree, but is
> > > disabled, then its PCI host bridge driver was not instantiated.
> > > This results in the failure of the pci_get_host_bridge_segment()
> > > and the following panic during Xen start:
> > >
> > > (XEN) Device tree generation failed (-22).
> > > (XEN)
> > > (XEN) ****************************************
> > > (XEN) Panic on CPU 0:
> > > (XEN) Could not set up DOM0 guest OS
> > > (XEN) ****************************************
> > >
> > > Fix this by adding "linux,pci-domain" property for all device tree nodes
> > > which have "pci" device type, so we know which segments will be used by
> > > the guest for which bridges.
> > >
> > > Fixes: 4cfab4425d39 ("xen/arm: Add linux,pci-domain property for hwdom if not 
> > > available.")
> > >
> > > Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > >
> > > ---
> > > New in v6
> > > ---
> > >    xen/arch/arm/domain_build.c        | 15 ++++++++++++++-
> > >    xen/arch/arm/pci/pci-host-common.c |  2 +-
> > >    xen/include/asm-arm/pci.h          |  8 ++++++++
> > >    3 files changed, 23 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > > index 491f5e2c316e..f7fcb1400c19 100644
> > > --- a/xen/arch/arm/domain_build.c
> > > +++ b/xen/arch/arm/domain_build.c
> > > @@ -753,9 +753,22 @@ static int __init write_properties(struct domain *d, 
> > > struct kernel_info *kinfo,
> > >            {
> > >                uint16_t segment;
> > >    +            /*
> > > +             * The node doesn't have "linux,pci-domain" property and it is
> > > +             * possible that:
> > > +             *  - Xen only has drivers for a part of the host bridges
> > > +             *  - some host bridges are disabled
> > > +             * Make sure we insert the correct "linux,pci-domain" property
> > > +             * in any case, so we know which segments will be used
> > > +             * by Linux for which bridges.
> > The check above will check the node type is "pci". AFAICT, this would also cover PCI 
> > devices. I am not aware of any issue to add "linux,pci-domain" for them. However, this 
> > feels a bit odd.
> >
> >  From my understanding, a PCI device would always be described as a child of the 
> > hostbridges. So I would rework the 'if' to also check if the parent type is not 
> > "pci".
> We may have "bridge -> bridge -> device" topology as well.
Do you have an example of Device-Tree?

> So, I prefer to have the check as it is.
I don't really like the idea to spuriously add "linux,pci-domain" to PCI 
DT node. But if there are no other solution, then this should at least 
be mentionned in the commit message and code.
[...]

> Yes, this sounds reasonable, I will add this change and print an error message 
> so it is
> easier to understand what Xen doesn't like (it took me a while to debug and 
> understand
> why I have "(XEN) Device tree generation failed (-22).")

Sounds good to me. The current error is indeed confusing.

Cheers,

--
Julien Grall