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

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Date:   Thu, 14 Sep 2023 14:53:53 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     James Morse <james.morse@....com>
CC:     <linux-pm@...r.kernel.org>, <loongarch@...ts.linux.dev>,
        <linux-acpi@...r.kernel.org>, <linux-arch@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-riscv@...ts.infradead.org>, <kvmarm@...ts.linux.dev>,
        <x86@...nel.org>, Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        <jianyong.wu@....com>, <justin.he@....com>
Subject: Re: [RFC PATCH v2 15/35] ACPI: processor: Add support for
 processors described as container packages

On Wed, 13 Sep 2023 16:38:03 +0000
James Morse <james.morse@....com> 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.
> 

Specification reference needed...

Terminology wise, I'd just refer to Processor() objects as I think they
are named objects rather than data terms like a package (Which include
a PkgLength etc)



> 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.

processor terms in a processor container. 
> 
> Signed-off-by: James Morse <james.morse@....com>

Otherwise looks fine to me.

Jonathan
> ---
>  drivers/acpi/acpi_processor.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> 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;
>  }
>