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Re: [PATCH for 6.2 v2 4/5] hw/i386/acpi-build: Deny control on PCIe Nati


From: Ani Sinha
Subject: Re: [PATCH for 6.2 v2 4/5] hw/i386/acpi-build: Deny control on PCIe Native Hot-plug in _OSC
Date: Thu, 11 Nov 2021 11:19:30 +0530 (IST)
User-agent: Alpine 2.22 (DEB 394 2020-01-19)


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.

> -    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
>
>



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