intel_sibling.c

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/* SPDX-License-Identifier: GPL-2.0-only */
 
#include <arch/cpu.h>
#include <console/console.h>
#include <cpu/intel/hyperthreading.h>
#include <device/device.h>
#include <option.h>
 
/* Intel hyper-threading requires serialized CPU init. */
 
static int first_time = 1;
static int disable_siblings = !CONFIG(LOGICAL_CPUS);
 
void intel_sibling_init(struct device *cpu)
{
        unsigned int i, siblings;
        struct cpuid_result result;
 
        /* On the bootstrap processor see if I want sibling cpus enabled */
        if (first_time) {
                first_time = 0;
                disable_siblings = get_uint_option("hyper_threading", disable_siblings);
        }
        result = cpuid(1);
        /* Is hyperthreading supported */
        if (!(result.edx & (1 << 28)))
                return;
 
        /* See how many sibling cpus we have */
        siblings = (result.ebx >> 16) & 0xff;
        if (siblings < 1)
                siblings = 1;
 
        printk(BIOS_DEBUG, "CPU: %u %d siblings\n",
                cpu->path.apic.apic_id,
                siblings);
 
        /* See if I am a sibling cpu */
        if (cpu->path.apic.apic_id & (siblings - 1)) {
                if (disable_siblings)
                        cpu->enabled = 0;
                return;
        }
 
        /* I am the primary CPU start up my siblings */
        for (i = 1; i < siblings; i++) {
                struct device_path cpu_path;
                struct device *new;
                /* Build the CPU device path */
                cpu_path.type = DEVICE_PATH_APIC;
                cpu_path.apic.apic_id = cpu->path.apic.apic_id + i;
 
                /* Allocate new CPU device structure iff sibling CPU
                 * was not in static device tree.
                 */
                new = alloc_find_dev(cpu->bus, &cpu_path);
 
                if (!new)
                        continue;
 
                printk(BIOS_DEBUG, "CPU: %u has sibling %u\n",
                        cpu->path.apic.apic_id,
                        new->path.apic.apic_id);
        }
}