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

[Igor Mammedov]

On Thu, 24 Sep 2020 09:00:06 +0200
Julia Suvorova <jusual@redhat.com> 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.

if I recall right, you had a idea about
 keeping pending removal request to distinguish between eject and poweroff
 (i.e. eject if mgmt asked for removal and otherwise it could be poweroff|nop)
 Why it didn't work out in the end?

>     * 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)
> 
> 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(-)
>