Hello,
Observation:
If we launch Linux Guest VM using QEMU(running on any type host. I am using
x86) with
CPU based on any ARM64 architecture then I could see QEMU populating ACPI nodes
related to same CPU at 2 places of the ACPI namespace:
1. \\_SB.CXXX
2. \\_SB.CPUS.CXXX
Above results in Guest VM showing duplicate CPU entries in the sysfs for the
same CPUS.
I could make out the entries under \\_SB.CPUS.XXX are part of the container.
estuary:/$ ls -al /sys/bus/acpi/devices/
Observation 1: (belongs to \\_SB.C00X)
ACPI0007:00 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:00
ACPI0007:01 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:01
ACPI0007:02 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:02
ACPI0007:03 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:03
ACPI0007:04 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:04
ACPI0007:05 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0007:05
Observation 2: (belongs to \\_SB.CPUS.C00X and under container ACPI0010:00 part
of \\_SB.CPUS)
ACPI0007:06 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:06
ACPI0007:07 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:07
ACPI0007:08 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:08
ACPI0007:09 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:09
ACPI0007:0a -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:0a
ACPI0007:0b -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00/ACPI0007:0b
ACPI0010:00 -> ../../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0010:00
estuary:/$ cat /sys/bus/acpi/devices/ACPI0010\:00/path
\_SB_.CPUS
estuary:/$ cat /sys/bus/acpi/devices/ACPI0007\:00/uid
0
estuary:/$ cat /sys/bus/acpi/devices/ACPI0007\:00/path
\_SB_.C000
estuary:/$ cat /sys/bus/acpi/devices/ACPI0007\:06/uid
0
estuary:/$ cat /sys/bus/acpi/devices/ACPI0007\:06/path
\_SB_.CPUS.C000
QEMU Code Excerpt:
I could trace with in QEMU AML code, the CPUS are being appended at 2 places:
Code 1. File: hw/arm/virt-acpi-build.c (Cause of Observation 1 i.e. \\_SB.CXXX )
static void acpi_dsdt_add_cpus(Aml *scope, int smp_cpus)
{
uint16_t i;
for (i = 0; i < smp_cpus; i++) { --->{should be possible cpus anyways}
Aml *dev = aml_device("C%.03X", i);
aml_append(dev, aml_name_decl("_HID", aml_string("ACPI0007")));
aml_append(dev, aml_name_decl("_UID", aml_int(i)));
aml_append(scope, dev);
}
}
Code 2. File: hw/acpi/cpu.c (Cause of Observation 2 i.e. \\_SB.CPUS.CXXX)
void build_cpus_aml(..)
{
[...]
cpus_dev = aml_device("\\_SB.CPUS");
{
[...]
/* build Processor object for each processor */
for (i = 0; i < arch_ids->len; i++) {
Aml *dev;
Aml *uid = aml_int(i);
GArray *madt_buf = g_array_new(0, 1, 1);
int arch_id = arch_ids->cpus[i].arch_id;
if (opts.acpi_1_compatible && arch_id < 255) {
dev = aml_processor(i, 0, 0, CPU_NAME_FMT, i);
} else {
dev = aml_device(CPU_NAME_FMT, i);
aml_append(dev, aml_name_decl("_HID", aml_string("ACPI0007")));
aml_append(dev, aml_name_decl("_UID", uid));
}
[...]
}
[...]
}
Questions:
Q1. I could not understand the purpose of keeping acpi_dsdt_add_cpus() after
the code 2.
was introduced as part of the below change and which is already adding
CPUS related
AML to \\_SB.CPUS namespace?
acpi: cpuhp: add CPU devices AML with _STA method
commit 5e1b5d93887b52eede156f846b6c4c5c8bbcfcdb
Q2. Do we really require CPUs being added by acpi_dsdt_add_cpus() in \\_SB.CXXX
Namespace OR is it a stray code left?
Please help to correct if there is a gap in my understanding here and please
forgive me if I have terribly missed out something very basic here.
Many thanks!
Best Regards
Salil
