|
| From: | Ani Sinha |
| Subject: | Re: [RFC PATCH v3 0/7] Use ACPI PCI hot-plug for Q35 |
| Date: | Thu, 1 Oct 2020 21:41:29 +0530 |
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.
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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