Re: [PATCH V13 4/8] hw/acpi: Update GED _EVT method AML with CPU scan

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 7 Jun 2024 12:56:45 +0100
Salil Mehta <salil.mehta@huawei.com> wrote:

> OSPM evaluates _EVT method to map the event. The CPU hotplug event eventually
> results in start of the CPU scan. Scan figures out the CPU and the kind of
> event(plug/unplug) and notifies it back to the guest. Update the GED AML _EVT
> method with the call to \\_SB.CPUS.CSCN
> 
> Also, macro CPU_SCAN_METHOD might be referred in other places like during GED
> intialization so it makes sense to have its definition placed in some common
> header file like cpu_hotplug.h. But doing this can cause compilation break
> because of the conflicting macro definitions present in cpu.c and cpu_hotplug.c

one of the reasons is that you reusing legacy hw/acpi/cpu_hotplug.h,
see below for suggestion.

> and because both these files get compiled due to historic reasons of x86 world
> i.e. decision to use legacy(GPE.2)/modern(GED) CPU hotplug interface happens
> during runtime [1]. To mitigate above, for now, declare a new common macro
> ACPI_CPU_SCAN_METHOD for CPU scan method instead.
> (This needs a separate discussion later on for clean-up)
> 
> Reference:
> [1] https://lore.kernel.org/qemu-devel/1463496205-251412-24-git-send-email-imammedo@redhat.com/
> 
> Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Tested-by: Xianglai Li <lixianglai@loongson.cn>
> Tested-by: Miguel Luis <miguel.luis@oracle.com>
> Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
> Tested-by: Zhao Liu <zhao1.liu@intel.com>
> ---
>  hw/acpi/cpu.c                  | 2 +-
>  hw/acpi/generic_event_device.c | 4 ++++
>  include/hw/acpi/cpu_hotplug.h  | 2 ++
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
> index 473b37ba88..af2b6655d2 100644
> --- a/hw/acpi/cpu.c
> +++ b/hw/acpi/cpu.c
> @@ -327,7 +327,7 @@ const VMStateDescription vmstate_cpu_hotplug = {
>  #define CPUHP_RES_DEVICE  "PRES"
>  #define CPU_LOCK          "CPLK"
>  #define CPU_STS_METHOD    "CSTA"
> -#define CPU_SCAN_METHOD   "CSCN"
> +#define CPU_SCAN_METHOD   ACPI_CPU_SCAN_METHOD
>  #define CPU_NOTIFY_METHOD "CTFY"
>  #define CPU_EJECT_METHOD  "CEJ0"
>  #define CPU_OST_METHOD    "COST"
> diff --git a/hw/acpi/generic_event_device.c b/hw/acpi/generic_event_device.c
> index 54d3b4bf9d..63226b0040 100644
> --- a/hw/acpi/generic_event_device.c
> +++ b/hw/acpi/generic_event_device.c
> @@ -109,6 +109,10 @@ void build_ged_aml(Aml *table, const char *name, HotplugHandler *hotplug_dev,
>                  aml_append(if_ctx, aml_call0(MEMORY_DEVICES_CONTAINER "."
>                                               MEMORY_SLOT_SCAN_METHOD));
>                  break;
> +            case ACPI_GED_CPU_HOTPLUG_EVT:
> +                aml_append(if_ctx, aml_call0(ACPI_CPU_CONTAINER "."
> +                                             ACPI_CPU_SCAN_METHOD));

I don't particularly like exposing cpu hotplug internals for outside code
and then making that code do plumbing hoping that nothing will explode
in the future.

build_cpus_aml() takes event_handler_method to create a method that
can be called by platform. What I suggest is to call that method here
instead of trying to expose CPU hotplug internals and manually building
call path here.
aka:
  build_cpus_aml(event_handler_method = PATH_TO_GED_DEVICE.CSCN)
and then call here 
  aml_append(if_ctx, aml_call0(CSCN));
which will call  CSCN in GED scope, that was be populated by
build_cpus_aml() to do cpu scan properly without need to expose
cpu hotplug internal names and then trying to fixup conflicts caused by that.

PS:
we should do the same for memory hotplug, we see in context above


> +                break;
>              case ACPI_GED_PWR_DOWN_EVT:
>                  aml_append(if_ctx,
>                             aml_notify(aml_name(ACPI_POWER_BUTTON_DEVICE),
> diff --git a/include/hw/acpi/cpu_hotplug.h b/include/hw/acpi/cpu_hotplug.h
> index 48b291e45e..ef631750b4 100644
> --- a/include/hw/acpi/cpu_hotplug.h
> +++ b/include/hw/acpi/cpu_hotplug.h
> @@ -20,6 +20,8 @@
>  #include "hw/acpi/cpu.h"
>  
>  #define ACPI_CPU_HOTPLUG_REG_LEN 12
> +#define ACPI_CPU_SCAN_METHOD "CSCN"
> +#define ACPI_CPU_CONTAINER "\\_SB.CPUS"
>  
>  typedef struct AcpiCpuHotplug {
>      Object *device;