Re: [RFC PATCH v3 0/7] Use ACPI PCI hot-plug for Q35

[Ani Sinha <ani@anisinha.ca>]

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On Thu, Oct 1, 2020 at 9:24 PM Julia Suvorova <jusual@redhat.com> wrote:

> On Thu, Oct 1, 2020 at 1:40 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> >
>
> > On Thu, Oct 01, 2020 at 10:55:35AM +0200, Julia Suvorova wrote:
>
> > > On Thu, Sep 24, 2020 at 11:20 AM Michael S. Tsirkin <mst@redhat.com>
> wrote:
>
> > > >
>
> > > > On Thu, Sep 24, 2020 at 09:00:06AM +0200, Julia Suvorova wrote:
>
> > > > > The patch set consists of two parts:
>
> > > > > patches 1-4: introduce new feature
>
> > > > >              'acpi-pci-hotplug-with-bridge-support' on Q35
>
> > > > > patches 5-7: make the feature default along with changes in ACPI
> tables
>
> > > > >
>
> > > > > This way maintainers can decide which way to choose without
> breaking
>
> > > > > the patch set.
>
> > > > >
>
> > > > > With the feature disabled Q35 falls back to the native hot-plug.
>
> > > > >
>
> > > > > Pros
>
> > > > >     * no racy behavior during boot (see 110c477c2ed)
>
> > > > >     * eject is possible - according to PCIe spec, attention button
>
> > > > >       press should lead to power off, and then the adapter should
> be
>
> > > > >       removed manually. As there is no power down state exists in
> QEMU,
>
> > > > >       we cannot distinguish between an eject and a power down
>
> > > > >       request.
>
> > > > >     * no delay during deleting - after the actual power off
> software
>
> > > > >       must wait at least 1 second before indicating about it. This
> case
>
> > > > >       is quite important for users, it even has its own bug:
>
> > > > >           https://bugzilla.redhat.com/show_bug.cgi?id=1594168
>
> > > > >     * no timer-based behavior - in addition to the previous
> example,
>
> > > > >       the attention button has a 5-second waiting period, during
> which
>
> > > > >       the operation can be canceled with a second press. While this
>
> > > > >       looks fine for manual button control, automation will result
> in
>
> > > > >       the need to queue or drop events, and the software receiving
>
> > > > >       events in all sort of unspecified combinations of
> attention/power
>
> > > > >       indicator states, which is racy and uppredictable.
>
> > > > >     * fixes:
>
> > > > >         * https://bugzilla.redhat.com/show_bug.cgi?id=1752465
>
> > > > >         * https://bugzilla.redhat.com/show_bug.cgi?id=1690256
>
> > > > >
>
> > > > > Cons:
>
> > > > >     * lose per-port control over hot-plug (can be resolved)
>
> > > > >     * no access to possible features presented in slot capabilities
>
> > > > >       (this is only surprise removal AFAIK)
>
> > > >
>
> > > > something I don't quite get is whether with this one can still add
>
> > > > new pcie bridges and then hotplug into these with native
>
> > > > hotplug.
>
> > >
>
> > > Right now I disable native if there is acpihp anywhere, but even if
>
> > > you enable it for hotplugged devices, native hot-plug will not work.
>
> >
>
> > So that's a minor regression in functionality, right?
>
> > Why is that the case? Because you disable it in ACPI?
>
> > What if we don't?
>
>
>
> I meant that I disable slot hotplug capabilities, nothing in ACPI
>
> prevents native from working. Actually, I don't see if there's any
>
> regression at all. Configurations like hot-plugging downstream port or
>
> switch to another downstream port haven't worked before, and they
>
> don't work now. I can enable native for hotplugged bridges, but that
>
> doesn't make sense, because you won't be able to hot-plug anything to
>
> it.


Why is that?

It's not an issue of ACPI, it's PCIe behaviour. Also, native-acpi
>
> combination may seem bizarre to os (slot enumeration is independent,
>
> that's why I suggested disabling pcie slot flags).
>
>
>
> > > > the challenge to answering this with certainty is that right now qemu
>
> > > > does not allow hotplugging complex devices such as bridges at all,
>
> > > > we only have a hack for multifunction devices.
>
> > > > Maybe adding a bridge as function 1 on command line, then
> hotplugging another device as
>
> > > > function 0 will work to test this.
>
> > > >
>
> > > >
>
> > > >
>
> > > > > v3:
>
> > > > >     * drop change of _OSC to allow SHPC on hotplugged bridges
>
> > > > >     * use 'acpi-root-pci-hotplug'
>
> > > > >     * add migration states [Igor]
>
> > > > >     * minor style changes
>
> > > > >
>
> > > > > v2:
>
> > > > >     * new ioport range for acpiphp [Gerd]
>
> > > > >     * drop find_pci_host() [Igor]
>
> > > > >     * explain magic numbers in _OSC [Igor]
>
> > > > >     * drop build_q35_pci_hotplug() wrapper [Igor]
>
> > > > >
>
> > > > > Julia Suvorova (7):
>
> > > > >   hw/acpi/pcihp: Enhance acpi_pcihp_disable_root_bus() to support
> Q35
>
> > > > >   hw/i386/acpi-build: Add ACPI PCI hot-plug methods to Q35
>
> > > > >   hw/pci/pcie: Do not initialize slot capability if acpihp is used
>
> > > > >   hw/acpi/ich9: Enable ACPI PCI hot-plug
>
> > > > >   bios-tables-test: Allow changes in DSDT ACPI tables
>
> > > > >   hw/acpi/ich9: Set ACPI PCI hot-plug as default
>
> > > > >   bios-tables-test: Update golden binaries
>
> > > > >
>
> > > > >  hw/i386/acpi-build.h              |   7 ++++
>
> > > > >  include/hw/acpi/ich9.h            |   5 +++
>
> > > > >  include/hw/acpi/pcihp.h           |   3 +-
>
> > > > >  hw/acpi/ich9.c                    |  67
> ++++++++++++++++++++++++++++++
>
> > > > >  hw/acpi/pcihp.c                   |  16 ++++---
>
> > > > >  hw/acpi/piix4.c                   |   4 +-
>
> > > > >  hw/i386/acpi-build.c              |  31 ++++++++------
>
> > > > >  hw/i386/pc.c                      |   1 +
>
> > > > >  hw/pci/pcie.c                     |  16 +++++++
>
> > > > >  tests/data/acpi/q35/DSDT          | Bin 7678 -> 7950 bytes
>
> > > > >  tests/data/acpi/q35/DSDT.acpihmat | Bin 9002 -> 9274 bytes
>
> > > > >  tests/data/acpi/q35/DSDT.bridge   | Bin 7695 -> 9865 bytes
>
> > > > >  tests/data/acpi/q35/DSDT.cphp     | Bin 8141 -> 8413 bytes
>
> > > > >  tests/data/acpi/q35/DSDT.dimmpxm  | Bin 9331 -> 9603 bytes
>
> > > > >  tests/data/acpi/q35/DSDT.ipmibt   | Bin 7753 -> 8025 bytes
>
> > > > >  tests/data/acpi/q35/DSDT.memhp    | Bin 9037 -> 9309 bytes
>
> > > > >  tests/data/acpi/q35/DSDT.mmio64   | Bin 8808 -> 9080 bytes
>
> > > > >  tests/data/acpi/q35/DSDT.numamem  | Bin 7684 -> 7956 bytes
>
> > > > >  tests/data/acpi/q35/DSDT.tis      | Bin 8283 -> 8555 bytes
>
> > > > >  19 files changed, 129 insertions(+), 21 deletions(-)
>
> > > > >
>
> > > > > --
>
> > > > > 2.25.4
>
> > > >
>
> >
>
>
>
>

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