Re: [RFC PATCH v2 15/35] ACPI: processor: Add support for processors described as container packages

[Gavin Shan <gshan@redhat.com>]

On 9/14/23 02:38, James Morse wrote:
> ACPI has two ways of describing processors in the DSDT. Either as a device
> object with HID ACPI0007, or as a type 'C' package inside a Processor
> Container. The ACPI processor driver probes CPUs described as devices, but
> not those described as packages.
> 
> Duplicate descriptions are not allowed, the ACPI processor driver already
> parses the UID from both devices and containers. acpi_processor_get_info()
> returns an error if the UID exists twice in the DSDT.
> 
> The missing probe for CPUs described as packages creates a problem for
> moving the cpu_register() calls into the acpi_processor driver, as CPUs
> described like this don't get registered, leading to errors from other
> subsystems when they try to add new sysfs entries to the CPU node.
> (e.g. topology_sysfs_init()'s use of topology_add_dev() via cpuhp)
> 
> To fix this, parse the processor container and call acpi_processor_add()
> for each processor that is discovered like this. The processor container
> handler is added with acpi_scan_add_handler(), so no detach call will
> arrive.
> 
> Qemu TCG describes CPUs using packages in a processor container.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>   drivers/acpi/acpi_processor.c | 22 ++++++++++++++++++++++
>   1 file changed, 22 insertions(+)
> 

I don't understand the last sentence of the commit log. QEMU
always have "ACPI0007" for the processor devices.

#define ACPI_PROCESSOR_DEVICE_HID      "ACPI0007"
#define ACPI_PROCESSOR_OBJECT_HID      "LNXCPU"

[gshan@gshan q]$ git grep ACPI0007
hw/acpi/cpu.c:                aml_append(dev, aml_name_decl("_HID", aml_string("ACPI0007")));
hw/arm/virt-acpi-build.c:        aml_append(dev, aml_name_decl("_HID", aml_string("ACPI0007")));
hw/riscv/virt-acpi-build.c:            aml_append(dev, aml_name_decl("_HID", aml_string("ACPI0007")));
[gshan@gshan q]$ git grep LNXCPU

> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index c0839bcf78c1..b4bde78121bb 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -625,9 +625,31 @@ static struct acpi_scan_handler processor_handler = {
>   	},
>   };
>   
> +static acpi_status acpi_processor_container_walk(acpi_handle handle,
> +						 u32 lvl,
> +						 void *context,
> +						 void **rv)
> +{
> +	struct acpi_device *adev;
> +	acpi_status status;
> +
> +	adev = acpi_get_acpi_dev(handle);
> +	if (!adev)
> +		return AE_ERROR;
> +
> +	status = acpi_processor_add(adev, &processor_device_ids[0]);
> +	acpi_put_acpi_dev(adev);
> +
> +	return status;
> +}
> +
>   static int acpi_processor_container_attach(struct acpi_device *dev,
>   					   const struct acpi_device_id *id)
>   {
> +	acpi_walk_namespace(ACPI_TYPE_PROCESSOR, dev->handle,
> +			    ACPI_UINT32_MAX, acpi_processor_container_walk,
> +			    NULL, NULL, NULL);
> +
>   	return 1;
>   }
>   

Thanks,
Gavin