linux-kernel - Re: [PATCH v2] LoongArch: Correct the calculation logic of thread

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Message-ID: <CAAhV-H6vmQpBhf5qiBg9C1SMSOy3O5hd6RnPc1B0Yg3r3+exSA@mail.gmail.com>
Date: Thu, 27 Nov 2025 15:36:20 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Qiang Ma <maqianga@...ontech.com>
Cc: kernel@...0n.name, hengqi.chen@...il.com, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] LoongArch: Correct the calculation logic of thread_count

Hi, Qiang,

On Thu, Nov 27, 2025 at 11:32 AM Qiang Ma <maqianga@...ontech.com> wrote:
>
> For thread_count, the current calculation method has a maximum of 255,
> which may not be sufficient in the future. Therefore, we are correcting
> it now.
>
> Reference: SMBIOS Specification, 7.5 Processor Information (Type 4)[1]
>
> [1]: https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_3.9.0.pdf
>
> Signed-off-by: Qiang Ma <maqianga@...ontech.com>
> ---
>  arch/loongarch/kernel/setup.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> index 25a87378e48e..8dd25fc4bd13 100644
> --- a/arch/loongarch/kernel/setup.c
> +++ b/arch/loongarch/kernel/setup.c
> @@ -56,6 +56,7 @@
>  #define SMBIOS_FREQLOW_MASK            0xFF
>  #define SMBIOS_CORE_PACKAGE_OFFSET     0x23
>  #define SMBIOS_THREAD_PACKAGE_OFFSET   0x25
> +#define SMBIOS_THREAD_PACKAGE_2_OFFSET 0x2E
>  #define LOONGSON_EFI_ENABLE            (1 << 3)
>
>  unsigned long fw_arg0, fw_arg1, fw_arg2;
> @@ -120,13 +121,19 @@ static void __init parse_cpu_table(const struct dmi_header *dm)
>  {
>         long freq_temp = 0;
>         char *dmi_data = (char *)dm;
> +       u8 thread_count;
>
>         freq_temp = ((*(dmi_data + SMBIOS_FREQHIGH_OFFSET) << 8) +
>                         ((*(dmi_data + SMBIOS_FREQLOW_OFFSET)) & SMBIOS_FREQLOW_MASK));
>         cpu_clock_freq = freq_temp * 1000000;
>
>         loongson_sysconf.cpuname = (void *)dmi_string_parse(dm, dmi_data[16]);
> -       loongson_sysconf.cores_per_package = *(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
> +       thread_count = *(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
> +       if (thread_count != 0)
> +               loongson_sysconf.cores_per_package =
> +                               dm->length >= 0x30 && thread_count == 0xFF ?
> +                               *(u16 *)(dmi_data + SMBIOS_THREAD_PACKAGE_2_OFFSET) :
> +                               thread_count;
According SPEC, it uses THREAD_COUNT_2 only if dm->length >= 30 and
thread_count == 0xff, so the correct and simplest way is like this:

        cpu_clock_freq = freq_temp * 1000000;

        loongson_sysconf.cpuname = (void *)dmi_string_parse(dm, dmi_data[16]);
-       loongson_sysconf.cores_per_package = *(dmi_data +
SMBIOS_THREAD_PACKAGE_OFFSET);
+       if (dm->length < 0x30)
+               thread_count = *(u8 *)(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
+       else if (thread_count == 0xff)
+               thread_count = *(u16 *)(dmi_data +
SMBIOS_THREAD_PACKAGE_2_OFFSET);
+       loongson_sysconf.cores_per_package = thread_count;

        pr_info("CpuClock = %llu\n", cpu_clock_freq);

Huacai

>
>         pr_info("CpuClock = %llu\n", cpu_clock_freq);
>  }
> --
> 2.20.1
>