[PATCH RFC v3 02/21] ACPI: processor: Add support for processors described as container packages

Russell King
2023-12-13T12:49:25Z

From: James Morse <james.morse@arm.com>

ACPI has two ways of describing processors in the DSDT. From ACPI v6.5,
5.2.12:

"Starting with ACPI Specification 6.3, the use of the Processor() object
was deprecated. Only legacy systems should continue with this usage. On
the Itanium architecture only, a _UID is provided for the Processor()
that is a string object. This usage of _UID is also deprecated since it
can preclude an OSPM from being able to match a processor to a
non-enumerable device, such as those defined in the MADT. From ACPI
Specification 6.3 onward, all processor objects for all architectures
except Itanium must now use Device() objects with an _HID of ACPI0007,
and use only integer _UID values."

Also see https://uefi.org/specs/ACPI/6.5/08_Processor_Configuration_and_Control.html#declaring-processors

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 processor devices in a processor container.
For more information, see build_cpus_aml() in Qemu hw/acpi/cpu.c and
https://uefi.org/specs/ACPI/6.5/08_Processor_Configuration_and_Control.html#processor-container-device

Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@arm.com>
---
Outstanding comments:
https://lore.kernel.org/r/20230914145353.000072e2@Huawei.com
https://lore.kernel.org/r/50571c2f-aa3c-baeb-3add-cd59e0eddc02@redhat.com
---
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 4fe2ef54088c..6a542e0ce396 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -626,9 +626,31 @@ 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;
}

--
2.30.2