Re: [RFC PATCH v4 0/7] Use ACPI PCI hot-plug for Q35

[Julia Suvorova]

On Sun, May 23, 2021 at 10:26 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Thu, May 13, 2021 at 08:26:35AM +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.
>
> Overall I think this version has addressed my concerns, good job!
> I see Igor has some suggestions on how to structure the code,
> they seem easy to address.
> Question: what makes this an RFC? Any known bugs/missing functionality?
> I don't see anything obvious - what did I miss?

No known issues, just indecisiveness about the default. The next
version will be non-RFC.

Best regards, Julia Suvorova.

> > 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 or reduces the likelihood of the bugs:
> >         * https://bugzilla.redhat.com/show_bug.cgi?id=1833187
> >         * https://bugzilla.redhat.com/show_bug.cgi?id=1657077
> >         * https://bugzilla.redhat.com/show_bug.cgi?id=1669931
> >         * https://bugzilla.redhat.com/show_bug.cgi?id=1678290
> >
> > Cons:
> >     * no access to possible features presented in slot capabilities
> >       (this is only surprise removal AFAIK)
> >
> > v4:
> >     * regain per-port control over hot-plug
> >     * rebased over acpi-index changes
> >     * set property on machine type to
> >       make pci code more generic [Igor, Michael]
> >
> > 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/acpi/ich9: Enable ACPI PCI hot-plug
> >   hw/pci/pcie: Do not set HPC flag if acpihp is used
> >   bios-tables-test: Allow changes in DSDT ACPI tables
> >   hw/acpi/ich9: Set ACPI PCI hot-plug as default on Q35
> >   bios-tables-test: Update golden binaries
> >
> >  hw/i386/acpi-build.h              |   5 +++
> >  include/hw/acpi/ich9.h            |   5 +++
> >  include/hw/acpi/pcihp.h           |   3 +-
> >  include/hw/boards.h               |   1 +
> >  hw/acpi/ich9.c                    |  68 ++++++++++++++++++++++++++++++
> >  hw/acpi/pcihp.c                   |  22 +++++++---
> >  hw/acpi/piix4.c                   |   4 +-
> >  hw/core/machine.c                 |  19 +++++++++
> >  hw/i386/acpi-build.c              |  32 ++++++++------
> >  hw/i386/pc.c                      |   4 +-
> >  hw/i386/pc_q35.c                  |   8 ++++
> >  hw/pci/pcie.c                     |  11 ++++-
> >  tests/data/acpi/q35/DSDT          | Bin 7859 -> 8289 bytes
> >  tests/data/acpi/q35/DSDT.acpihmat | Bin 9184 -> 9614 bytes
> >  tests/data/acpi/q35/DSDT.bridge   | Bin 7877 -> 11003 bytes
> >  tests/data/acpi/q35/DSDT.cphp     | Bin 8323 -> 8753 bytes
> >  tests/data/acpi/q35/DSDT.dimmpxm  | Bin 9513 -> 9943 bytes
> >  tests/data/acpi/q35/DSDT.ipmibt   | Bin 7934 -> 8364 bytes
> >  tests/data/acpi/q35/DSDT.memhp    | Bin 9218 -> 9648 bytes
> >  tests/data/acpi/q35/DSDT.mmio64   | Bin 8990 -> 9419 bytes
> >  tests/data/acpi/q35/DSDT.nohpet   | Bin 7717 -> 8147 bytes
> >  tests/data/acpi/q35/DSDT.numamem  | Bin 7865 -> 8295 bytes
> >  tests/data/acpi/q35/DSDT.tis      | Bin 8465 -> 8894 bytes
> >  23 files changed, 161 insertions(+), 21 deletions(-)
> >
> > --
> > 2.30.2
>