Re: [PATCH for 6.2 v2 4/5] hw/i386/acpi-build: Deny control on PCIe Native Hot-plug in _OSC

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 11 Nov 2021 11:19:30 +0530 (IST)
Ani Sinha <ani@anisinha.ca> wrote:

> On Wed, 10 Nov 2021, Igor Mammedov wrote:
> 
> > From: Julia Suvorova <jusual@redhat.com>
> >
> > There are two ways to enable ACPI PCI Hot-plug:
> >
> >         * Disable the Hot-plug Capable bit on PCIe slots.
> >
> > This was the first approach which led to regression [1-2], as
> > I/O space for a port is allocated only when it is hot-pluggable,
> > which is determined by HPC bit.
> >
> >         * Leave the HPC bit on and disable PCIe Native Hot-plug in _OSC
> >           method.
> >
> > This removes the (future) ability of hot-plugging switches with PCIe
> > Native hotplug since ACPI PCI Hot-plug only works with cold-plugged
> > bridges. If the user wants to explicitely use this feature, they can
> > disable ACPI PCI Hot-plug with:
> >         --global ICH9-LPC.acpi-pci-hotplug-with-bridge-support=off
> >
> > Change the bit in _OSC method so that the OS selects ACPI PCI Hot-plug
> > instead of PCIe Native.
> >
> > [1] https://gitlab.com/qemu-project/qemu/-/issues/641
> > [2] https://bugzilla.redhat.com/show_bug.cgi?id=2006409
> >
> > Signed-off-by: Julia Suvorova <jusual@redhat.com>
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> > v2:
> >   - (mst)
> >       * drop local hotplug var and opencode it
> >       * rename acpi_pcihp parameter to enable_native_pcie_hotplug
> >         to reflect what it actually does
> >
> > tested:
> >   with hotplugging nic into 1 root port with seabios/ovmf/Fedora34
> >   Windows tested only with seabios (using exiting images)
> >   (installer fails to install regardless on bios)
> > ---
> >  hw/i386/acpi-build.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index a3ad6abd33..a99c6e4fe3 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -1337,7 +1337,7 @@ static void build_x86_acpi_pci_hotplug(Aml *table, uint64_t pcihp_addr)
> >      aml_append(table, scope);
> >  }
> >
> > -static Aml *build_q35_osc_method(void)
> > +static Aml *build_q35_osc_method(bool enable_native_pcie_hotplug)
> >  {
> >      Aml *if_ctx;
> >      Aml *if_ctx2;
> > @@ -1359,8 +1359,10 @@ static Aml *build_q35_osc_method(void)
> >      /*
> >       * Always allow native PME, AER (no dependencies)
> >       * Allow SHPC (PCI bridges can have SHPC controller)
> > +     * Disable PCIe Native Hot-plug if ACPI PCI Hot-plug is enabled.
> >       */  
> 
> Based on v2, I think its more useful to have this comment where the
> function is called.
I'd leave it as is, which is consistent with other bits described here

> 
> > -    aml_append(if_ctx, aml_and(a_ctrl, aml_int(0x1F), a_ctrl));
> > +    aml_append(if_ctx, aml_and(a_ctrl,
> > +        aml_int(0x1E | (enable_native_pcie_hotplug ? 0x1 : 0x0)), a_ctrl));
> >
> >      if_ctx2 = aml_if(aml_lnot(aml_equal(aml_arg(1), aml_int(1))));
> >      /* Unknown revision */
> > @@ -1449,7 +1451,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> >          aml_append(dev, aml_name_decl("_CID", aml_eisaid("PNP0A03")));
> >          aml_append(dev, aml_name_decl("_ADR", aml_int(0)));
> >          aml_append(dev, aml_name_decl("_UID", aml_int(pcmc->pci_root_uid)));
> > -        aml_append(dev, build_q35_osc_method());
> > +        aml_append(dev, build_q35_osc_method(!pm->pcihp_bridge_en));  
> 
> See above. I think it helps to add a comment here saying native hotplug is
> enabled when acpi hotplug is disabled for cold plugged bridges.
> 
> 
> >          aml_append(sb_scope, dev);
> >          if (mcfg_valid) {
> >              aml_append(sb_scope, build_q35_dram_controller(&mcfg));
> > @@ -1565,7 +1567,9 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> >              if (pci_bus_is_express(bus)) {
> >                  aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A08")));
> >                  aml_append(dev, aml_name_decl("_CID", aml_eisaid("PNP0A03")));
> > -                aml_append(dev, build_q35_osc_method());
> > +
> > +                /* Expander bridges do not have ACPI PCI Hot-plug enabled */
> > +                aml_append(dev, build_q35_osc_method(true));
> >              } else {
> >                  aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A03")));
> >              }
> > --
> > 2.27.0
> >
> >  
>