From: Julien Grall <julien.grall.oss@gmail.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: "Rahul Singh" <rahul.singh@arm.com>,
"Andrew Cooper" <andrew.cooper3@citrix.com>,
"Bertrand Marquis" <Bertrand.Marquis@arm.com>,
"Jan Beulich" <jbeulich@suse.com>,
xen-devel <xen-devel@lists.xenproject.org>, nd <nd@arm.com>,
"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [RFC PATCH v1 1/4] arm/pci: PCI setup and PCI host bridge discovery within XEN on ARM.
Date: Fri, 24 Jul 2020 20:24:23 +0100 [thread overview]
Message-ID: <CAJ=z9a3dXSnEBvhkHkZzV9URAGqSfdtJ1Lc838h_ViAWG3ZO4g@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.21.2007241127480.17562@sstabellini-ThinkPad-T480s>
On Fri, 24 Jul 2020 at 19:32, Stefano Stabellini <sstabellini@kernel.org> wrote:
> > If they are not equal, then I fail to see why it would be useful to have this
> > value in Xen.
>
> I think that's because the domain is actually more convenient to use
> because a segment can span multiple PCI host bridges. So my
> understanding is that a segment alone is not sufficient to identify a
> host bridge. From a software implementation point of view it would be
> better to use domains.
AFAICT, this would be a matter of one check vs two checks in Xen :).
But... looking at Linux, they will also use domain == segment for ACPI
(see [1]). So, I think, they still have to use (domain, bus) to do the lookup.
>
> > In which case, we need to use PHYSDEVOP_pci_mmcfg_reserved so
> > Dom0 and Xen can synchronize on the segment number.
>
> I was hoping we could write down the assumption somewhere that for the
> cases we care about domain == segment, and error out if it is not the
> case.
Given that we have only the domain in hand, how would you enforce that?
From this discussion, it also looks like there is a mismatch between the
implementation and the understanding on QEMU devel. So I am a bit
concerned that this is not stable and may change in future Linux version.
IOW, we are know tying Xen to Linux. So could we implement
PHYSDEVOP_pci_mmcfg_reserved *or* introduce a new property that
really represent the segment?
Cheers,
[1] https://elixir.bootlin.com/linux/latest/source/arch/arm64/kernel/pci.c#L74
Cheers,
next prev parent reply other threads:[~2020-07-24 19:25 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-23 15:40 [RFC PATCH v1 0/4] PCI devices passthrough on Arm Rahul Singh
2020-07-23 15:40 ` [RFC PATCH v1 1/4] arm/pci: PCI setup and PCI host bridge discovery within XEN on ARM Rahul Singh
2020-07-23 23:38 ` Stefano Stabellini
2020-07-24 7:03 ` Oleksandr Andrushchenko
2020-07-24 8:05 ` Julien Grall
2020-07-24 17:47 ` Stefano Stabellini
2020-07-27 15:27 ` Rahul Singh
2020-07-27 15:20 ` Rahul Singh
2020-07-24 8:44 ` Julien Grall
2020-07-24 17:41 ` Stefano Stabellini
2020-07-24 18:21 ` Julien Grall
2020-07-24 18:32 ` Stefano Stabellini
2020-07-24 19:24 ` Julien Grall [this message]
2020-07-24 23:46 ` Stefano Stabellini
2020-07-25 9:59 ` Julien Grall
2020-07-27 11:06 ` Roger Pau Monné
2020-07-28 0:06 ` Stefano Stabellini
2020-07-28 8:33 ` Roger Pau Monné
2020-07-28 18:33 ` Stefano Stabellini
2020-07-26 7:01 ` Jan Beulich
2020-07-27 13:27 ` Rahul Singh
2020-07-24 8:23 ` Julien Grall
2020-07-27 15:29 ` Rahul Singh
2020-07-24 14:44 ` Roger Pau Monné
2020-07-24 15:15 ` Julien Grall
2020-07-24 15:29 ` Roger Pau Monné
2020-07-24 15:42 ` Roger Pau Monné
2020-07-24 15:46 ` Julien Grall
2020-07-24 16:01 ` Jan Beulich
2020-07-24 16:54 ` Julien Grall
2020-07-27 10:34 ` Roger Pau Monné
2020-07-28 8:06 ` Rahul Singh
2020-07-28 8:21 ` Roger Pau Monné
2020-07-23 15:40 ` [RFC PATCH v1 2/4] xen/arm: Discovering PCI devices and add the PCI devices in XEN Rahul Singh
2020-07-23 20:44 ` Stefano Stabellini
2020-07-24 7:14 ` Oleksandr Andrushchenko
2020-07-24 8:19 ` Julien Grall
2020-07-27 16:10 ` Rahul Singh
2020-07-24 14:49 ` Roger Pau Monné
2020-07-27 8:40 ` Rahul Singh
2020-07-23 15:40 ` [RFC PATCH v1 3/4] xen/arm: Enable the existing x86 virtual PCI support for ARM Rahul Singh
2020-07-23 23:39 ` Stefano Stabellini
2020-07-24 15:08 ` Roger Pau Monné
2020-07-23 15:40 ` [RFC PATCH v1 4/4] arm/libxl: Emulated PCI device tree node in libxl Rahul Singh
2020-07-23 23:39 ` Stefano Stabellini
2020-07-24 7:55 ` Oleksandr Andrushchenko
2020-07-24 9:11 ` Julien Grall
2020-07-27 13:40 ` Rahul Singh
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