/*
 * Copyright (C) 2021 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

/**
 * @file
 *
 * Memory map
 *
 */

#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include "ntloader.h"
#include "e820.h"

/** Buffer for INT 15,e820 calls */
static struct e820_entry e820_buf __attribute__ ((section (".bss16")));

/** Continuation value for next INT 15,e820 call */
static uint32_t e820_ebx;

/**
 * Get system memory map entry
 *
 * @v prev		Previous system memory map entry, or NULL at start
 * @v next		Next system memory map entry, or NULL at end
 */
struct e820_entry *memmap_next (struct e820_entry *prev)
{
    struct bootapp_callback_params params;

    /* Reset buffer and continuation value if restarting */
    if (! prev)
    {
        memset (&e820_buf, 0, sizeof (e820_buf));
        e820_ebx = 0;
    }
    else if (e820_ebx == 0)
    {
        /* Reach the end */
        return NULL;
    }

    /* Read system memory map */
    memset (&params, 0, sizeof (params));
    do
    {

        /* Call INT 15,e820 */
        params.vector.interrupt = 0x15;
        params.eax = 0xe820;
        params.ebx = e820_ebx;
        params.ecx = sizeof (e820_buf);
        params.edx = E820_SMAP;
        params.es = BASE_SEG;
        params.edi = (((void *) &e820_buf) -
                       ((void *) BASE_ADDRESS));
        call_interrupt (&params);

        /* Record continuation value */
        e820_ebx = params.ebx;

        /* Check result */
        if (params.eflags & CF)
        {
            DBG ("INT 15,e820 failed: error %02x\n", params.ah);
            break;
        }
        if (params.eax != E820_SMAP)
        {
            DBG ("INT 15,e820 invalid SMAP signature %08x\n",
                  params.eax);
            break;
        }
        DBG2 ("INT 15,e820 region [%llx,%llx) type %d\n",
               e820_buf.start, (e820_buf.start + e820_buf.len),
               e820_buf.type);

        /* Skip non-RAM regions */
        if (e820_buf.type != E820_TYPE_RAM)
            continue;
        if (params.ecx > offsetof (typeof (e820_buf), attrs))
        {
            if (! (e820_buf.attrs & E820_ATTR_ENABLED))
                continue;
            if (e820_buf.attrs & E820_ATTR_NONVOLATILE)
                continue;
        }

        /* Return this region */
        return &e820_buf;

    } while (e820_ebx != 0);

    return NULL;
}