src/cpu/intel/hyperthreading/intel_sibling.c

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2
   3 #include <console/console.h>
   4 #include <cpu/cpu.h>
   5 #include <cpu/intel/hyperthreading.h>
   6 #include <device/device.h>
   7 #include <option.h>
   8
   9 /* Intel hyper-threading requires serialized CPU init. */
  10
  11 static int first_time = 1;
  12 static int disable_siblings = !CONFIG(LOGICAL_CPUS);
  13
  14 void intel_sibling_init(struct device *cpu)
  15 {
  16         unsigned int i, siblings;
  17         struct cpuid_result result;
  18
  19         /* On the bootstrap processor see if I want sibling cpus enabled */
  20         if (first_time) {
  21                 first_time = 0;
  22                 disable_siblings = get_uint_option("hyper_threading", disable_siblings);
  23         }
  24         result = cpuid(1);
  25         /* Is hyperthreading supported */
  26         if (!(result.edx & (1 << 28)))
  27                 return;
  28
  29         /* See how many sibling cpus we have */
  30         siblings = (result.ebx >> 16) & 0xff;
  31         if (siblings < 1)
  32                 siblings = 1;
  33
  34         printk(BIOS_DEBUG, "CPU: %u %d siblings\n",
  35                 cpu->path.apic.apic_id,
  36                 siblings);
  37
  38         /* See if I am a sibling cpu */
  39         if (cpu->path.apic.apic_id & (siblings - 1)) {
  40                 if (disable_siblings)
  41                         cpu->enabled = 0;
  42                 return;
  43         }
  44
  45         /* I am the primary CPU start up my siblings */
  46         for (i = 1; i < siblings; i++) {
  47                 struct device_path cpu_path;
  48                 struct device *new;
  49                 /* Build the CPU device path */
  50                 cpu_path.type = DEVICE_PATH_APIC;
  51                 cpu_path.apic.apic_id = cpu->path.apic.apic_id + i;
  52
  53                 /* Allocate new CPU device structure iff sibling CPU
  54                  * was not in static device tree.
  55                  */
  56                 new = alloc_find_dev(cpu->bus, &cpu_path);
  57
  58                 if (!new)
  59                         continue;
  60
  61                 printk(BIOS_DEBUG, "CPU: %u has sibling %u\n",
  62                         cpu->path.apic.apic_id,
  63                         new->path.apic.apic_id);
  64         }
  65 }