/*
  StarForth — Steady-State Virtual Machine Runtime

  Copyright (c) 2023–2025 Robert A. James
  All rights reserved.

  This file is part of the StarForth project.

  Licensed under the StarForth License, Version 1.0 (the "License");
  you may not use this file except in compliance with the License.
*/

/**
 * acpi.c - Finding an ACPI table from the RSDP (FABRIC-3.10.8 MC-1b).
 * See starkernel/acpi.h. Moved out of arch/amd64/smp.c (MC-1a) when
 * aarch64 needed the same MADT lookup.
 */

#include "starkernel/acpi.h"

static int sig_eq(const uint8_t *p, const char *s, int n)
{
    int i;
    for (i = 0; i < n; i++) if (p[i] != (uint8_t)s[i]) return 0;
    return 1;
}

static uint32_t le32(const uint8_t *p)
{
    return (uint32_t)p[0] | ((uint32_t)p[1] << 8) | ((uint32_t)p[2] << 16) | ((uint32_t)p[3] << 24);
}

static uint64_t le64(const uint8_t *p)
{
    return (uint64_t)le32(p) | ((uint64_t)le32(p + 4) << 32);
}

uint32_t acpi_table_length(const uint8_t *table)
{
    return table ? le32(table + 4) : 0;
}

const uint8_t *acpi_find_table(const void *rsdp, const char *sig)
{
    const uint8_t *r = (const uint8_t *)rsdp;
    const uint8_t *xsdt;
    uint32_t len, n, i;

    /* RSDP: "RSD PTR " at 0, revision at 15, XSDT address at 24 (ACPI 2.0+). */
    if (!r || !sig_eq(r, "RSD PTR ", 8) || r[15] < 2) return (const uint8_t *)0;
    xsdt = (const uint8_t *)(uintptr_t)le64(r + 24);
    if (!xsdt || !sig_eq(xsdt, "XSDT", 4)) return (const uint8_t *)0;
    len = le32(xsdt + 4);
    if (len <= 36u) return (const uint8_t *)0;
    n = (len - 36u) / 8u;
    for (i = 0; i < n; i++) {
        const uint8_t *t = (const uint8_t *)(uintptr_t)le64(xsdt + 36u + 8u * i);
        if (t && sig_eq(t, sig, 4)) return t;
    }
    return (const uint8_t *)0;
}