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

["Michael S. Tsirkin" <mst@redhat.com>]

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.

This is in good shape, I think the next version can be a non-RFC series.

> 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 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