Re: [PATCH v2 02/25] hw/arm/virt: Introduce machine state acpi pcihp flags and props

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 27 May 2025 09:40:04 +0200
Eric Auger <eric.auger@redhat.com> wrote:

> acpi_pcihp VirtMachineClass state flag will allow
> to opt in for acpi pci hotplug. This is guarded by a

> class no_acpi_pcihp flag to manage compats (<= 10.0
> machine types will not support ACPI PCI hotplug).

there is no reason to put an effort in force disabling it
on old machines, as long as code works when explicitly
enabled property on CLI.

See comment below on how to deal with it 

> 
> Machine state acpi_pcihp flag must be set before the creation
> of the GED device which will use it.
> 
> Currently the ACPI PCI HP is turned off by default. This will
> change later on for 10.1 machine type.

one thing to note, is that turning it on by default might
cause change of NIC naming in guest as this brings in
new "_Sxx" slot naming. /so configs tied to nic  go down the drain/

Naming, we have, also happens to be broken wrt spec
(it should be unique system wide, there was a gitlab issue for that,
there is no easy fix that though)

So I'd leave it disabled by default and let users to turn
it on explicitly when needed. 

> 
> We also introduce properties to allow disabling it.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> Reviewed-by: Gustavo Romero <gustavo.romero@linaro.org>
> ---
>  include/hw/arm/virt.h |  2 ++
>  hw/arm/virt.c         | 27 +++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index 9a1b0f53d2..10ea581f06 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -129,6 +129,7 @@ struct VirtMachineClass {
>      bool no_tcg_lpa2;
>      bool no_ns_el2_virt_timer_irq;
>      bool no_nested_smmu;
> +    bool no_acpi_pcihp;
>  };
>  
>  struct VirtMachineState {
> @@ -150,6 +151,7 @@ struct VirtMachineState {
>      bool mte;
>      bool dtb_randomness;
>      bool second_ns_uart_present;
> +    bool acpi_pcihp;
>      OnOffAuto acpi;
>      VirtGICType gic_version;
>      VirtIOMMUType iommu;
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 9a6cd085a3..a0deeaf2b3 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2397,8 +2397,10 @@ static void machvirt_init(MachineState *machine)
>      create_pcie(vms);
>  
>      if (has_ged && aarch64 && firmware_loaded && virt_is_acpi_enabled(vms)) {
> +        vms->acpi_pcihp &= !vmc->no_acpi_pcihp;

I don't particularly like no_foo naming as it makes code harder to read
and combined with 'duplicated' field in machine state it make even things worse.
(if I recall right Philippe was cleaning mess similar flags usage
have introduced with ITS)

instead of adding machine property (both class and state),
I'd suggest adding the only property to GPE device (akin to what we have in x86 world)
And then one can meddle with defaults using hw_compat_xxx


>          vms->acpi_dev = create_acpi_ged(vms);
>      } else {
> +        vms->acpi_pcihp = false;
>          create_gpio_devices(vms, VIRT_GPIO, sysmem);
>      }
>  
> @@ -2593,6 +2595,20 @@ static void virt_set_its(Object *obj, bool value, Error **errp)
>      vms->its = value;
>  }
>  
> +static bool virt_get_acpi_pcihp(Object *obj, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    return vms->acpi_pcihp;
> +}
> +
> +static void virt_set_acpi_pcihp(Object *obj, bool value, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    vms->acpi_pcihp = value;
> +}
> +
>  static bool virt_get_dtb_randomness(Object *obj, Error **errp)
>  {
>      VirtMachineState *vms = VIRT_MACHINE(obj);
> @@ -3310,6 +3326,10 @@ static void virt_machine_class_init(ObjectClass *oc, const void *data)
>                                            "in ACPI table header."
>                                            "The string may be up to 8 bytes in size");
>  
> +    object_class_property_add_bool(oc, "acpi-pcihp",
> +                                   virt_get_acpi_pcihp, virt_set_acpi_pcihp);
> +    object_class_property_set_description(oc, "acpi-pcihp",
> +                                          "Force ACPI PCI hotplug");
>  }
>  
>  static void virt_instance_init(Object *obj)
> @@ -3344,6 +3364,9 @@ static void virt_instance_init(Object *obj)
>          vms->tcg_its = true;
>      }
>  
> +    /* default disallows ACPI PCI hotplug */
> +    vms->acpi_pcihp = false;
> +
>      /* Default disallows iommu instantiation */
>      vms->iommu = VIRT_IOMMU_NONE;
>  
> @@ -3394,8 +3417,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(10, 1)
>  
>  static void virt_machine_10_0_options(MachineClass *mc)
>  {
> +    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
> +
>      virt_machine_10_1_options(mc);
>      compat_props_add(mc->compat_props, hw_compat_10_0, hw_compat_10_0_len);
> +    /* 10.0 and earlier do not support ACPI PCI hotplug */
> +    vmc->no_acpi_pcihp = true;
>  }
>  DEFINE_VIRT_MACHINE(10, 0)
>