Re: [PATCH v2 RESEND] loongarch: retrieve CPU package ID from PPTT when available

[Mingcong Bai]

Hi Rong,

在 2026/7/5 17:36, Rong Bao 写道:
> Currently, the LoongArch CPU topology initialization code calculates
> each core's package ID by dividing its physical ID by
> loongson_sysconf.cores_per_package. This relies on the assumption that
> cores_per_package counts in the same domain as physical IDs.
>
> On Loongson 3B6000 (XB612B0V_1.2), cores_per_package matches the visible
> core count -- 24 in this case. However, the physical IDs range from 0 to
> 31 in a noncontinuous fashion:
>
>          $ cat /proc/cpuinfo | grep -i -F 'global_id'
>          global_id               : 0
>          global_id               : 1
>          global_id               : 4
>          global_id               : 5
>          global_id               : 6
>          global_id               : 7
>          global_id               : 8
>          global_id               : 9
>          global_id               : 10
>          global_id               : 11
>          global_id               : 14
>          global_id               : 15
>          global_id               : 16
>          global_id               : 17
>          global_id               : 20
>          global_id               : 21
>          global_id               : 22
>          global_id               : 23
>          global_id               : 26
>          global_id               : 27
>          global_id               : 28
>          global_id               : 29
>          global_id               : 30
>          global_id               : 31
>
> Retrieve the exact package ID from ACPI PPTT when available, in the same
> style as retrieving the core ID and thread ID in parse_acpi_topology().
> Use this information in loongson_init_secondary() when PPTT readout is
> successful. The original division logic is kept as a fallback.
>
> Meanwhile, since some code paths like loongson3_cpufreq expect a
> continuous integer sequence of package IDs in [0, MAX_PACKAGES) when
> retrieving from cpu_data[], we also canonicalize the package ID to be
> filled in parse_acpi_topology() to meet such an expectation.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Co-developed-by: Xi Ruoyao <xry111@xxxxxxxxxxx>
> Signed-off-by: Xi Ruoyao <xry111@xxxxxxxxxxx>
> Signed-off-by: Rong Bao <rong.bao@xxxxxxxxxxxx>
Tested good on my Loongson XB612B0_V1.0 with an 8-core 3B6000:

Architecture:                loongarch64
  CPU op-mode(s):            32-bit, 64-bit
  Address sizes:             48 bits physical, 48 bits virtual
  Byte Order:                Little Endian
CPU(s):                      16
  On-line CPU(s) list:       0-15
Model name:                  Loongson-3B6000
  CPU family:                Loongson-64bit
  Model:                     0x10
  Thread(s) per core:        2
  Core(s) per socket:        8
  Socket(s):                 1
  BogoMIPS:                  4600.00
  Flags:                     cpucfg lam lam_bh scq ual fpu lsx lasx 
crc32 complex crypto lspw lvz lbt_x86 lbt_arm lbt_mips
Caches (sum of all):
  L1d:                       512 KiB (8 instances)
  L1i:                       512 KiB (8 instances)
  L2:                        2 MiB (8 instances)
  L3:                        32 MiB (1 instance)
NUMA:
  NUMA node(s):              1
  NUMA node0 CPU(s):         0-15
Vulnerabilities:
  Gather data sampling:      Not affected
  Ghostwrite:                Not affected
  Indirect target selection: Not affected
  Itlb multihit:             Not affected
  L1tf:                      Not affected
  Mds:                       Not affected
  Meltdown:                  Not affected
  Mmio stale data:           Not affected
  Old microcode:             Not affected
  Reg file data sampling:    Not affected
  Retbleed:                  Not affected
  Spec rstack overflow:      Not affected
  Spec store bypass:         Not affected
  Spectre v1:                Mitigation; __user pointer sanitization
  Spectre v2:                Not affected
  Srbds:                     Not affected
  Tsa:                       Not affected
  Tsx async abort:           Not affected
  Vmscape:                   Not affected

With that:

Tested-by: Mingcong Bai <jeffbai@xxxxxxx>

Best Regards,
Mingcong Bai