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

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Message-ID: <B2E7E43661ACD241+64a342c7-66c0-4564-92c9-405bc0cd911b@uniontech.com>
Date: Thu, 27 Nov 2025 16:56:22 +0800
From: Qiang Ma <maqianga@...ontech.com>
To: Huacai Chen <chenhuacai@...nel.org>
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


在 2025/11/27 15:36, Huacai Chen 写道:
> 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);
Yes, this one should need to be converted:
thread_count = *(u8 *)(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;

This patch method refers to dmidecode, which is the same as it, like this:

                         if (data[0x25] != 0)
                                 pr_attr("Thread Count", "%u",
                                         h->length >= 0x30 && data[0x25] 
== 0xFF ?

                                         WORD(data + 0x2E) : data[0x25]);


> 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);
I feel there is a problem with this method.
I saw on the 3C6000/Q machine a few days ago that the dm->lenght is 0x30,
but only one byte is used, and the thread_count is 128, not 0xFF.
Is the initialization thread_count = *(u8 *)(dmi_data + 
SMBIOS_THREAD_PACKAGE_OFFSET) missing?
Wouldn't it be better to change it this way?

+       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 = *(u8 *)(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
+       if (thread_count == 0xFF && dm->length >= 0x30)
+               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
>>