/*
 * Copyright (c) 2023 Ian Marco Moffett and the Osmora Team.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of Hyra nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <machine/tss.h>
#include <machine/cpu.h>
#include <lib/string.h>
#include <vm/dynalloc.h>
#include <sys/panic.h>

__MODULE_NAME("TSS");
__KERNEL_META("$Hyra$: tss.c, Ian Marco Moffett, "
              "AMD64 Task state segment code");

static void
alloc_resources(struct cpu_info *cpu)
{
    struct tss_entry *tss;

    /*
     * Allocate TSS entries for this CPU
     */
    if (cpu->tss == NULL) {
        /* Allocate a TSS for this CPU */
        tss = dynalloc(sizeof(*tss));
        if (tss == NULL)
            panic("Failed to alloc %d bytes for TSS\n", sizeof(*tss));
        memset(tss, 0, sizeof(*tss));
        cpu->tss = tss;
    }
}

void
write_tss(struct cpu_info *cpu, struct tss_desc *desc)
{
    uintptr_t tss_base;

    alloc_resources(cpu);

    tss_base = (uintptr_t)cpu->tss;

    /*
     * XXX: The AVL (Available for use by system software)
     *      bit is ignored by hardware and it is up to us
     *      to decide how to use it... As of now, it is useless
     *      to us and shall remain 0.
     */
    desc->p = 1;        /* Must be present to be valid! */
    desc->g = 0;        /* Granularity -> 0 */
    desc->avl = 0;      /* Not used */
    desc->dpl = 0;      /* Descriptor Privilege Level -> 0 */
    desc->type = 0x9;   /* For TSS -> 0x9 (0b1001) */

    desc->base_lo16 = __SHIFTOUT(tss_base, __MASK(16));
    desc->base_mid24 = __SHIFTOUT(tss_base, __MASK(8) << 24);
    desc->base_mid32 = __SHIFTOUT(tss_base, __MASK(32) << 32);
}