mmap_boot.c

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/* SPDX-License-Identifier: GPL-2.0-or-later */
 
#include <boot_device.h>
#include <commonlib/region.h>
#include <console/console.h>
#include <fmap.h>
#include <intelblocks/fast_spi.h>
#include <spi_flash.h>
 
/*
 * BIOS region on the flash is mapped right below 4GiB in the address
 * space. However, 256KiB right below 4GiB is decoded by read-only SRAM and not
 * boot media.
 *
 *                                                +-----------+ 0
 *                                                |           |
 *                                                |           |
 *                                                |           |
 *                                                |           |
 *                                                |           |
 *                                                |           |
 *                                                |           |
 *                                                |           |
 *                  +--------+                    |           |
 *                  |  IFD   |                    |           |
 * bios_start +---> +--------+------------------> +-----------+ 4GiB - bios_size
 *     ^            |        |          ^         |           |
 *     |            |        |          |         |           |
 *     |            |        |  bios_mapped_size  |    BIOS   |
 *     |            |  BIOS  |          |         |           |
 * bios_size        |        |          |         |           |
 *     |            |        |          v         |           |
 *     |            |        +------------------> +-----------+ 4GiB - 256KiB
 *     |            |        |                    | Read only |
 *     v            |        |                    |    SRAM   |
 * bios_end   +---> +--------+                    +-----------+ 4GiB
 *                  | Device |
 *                  |   ext  |
 *                  +--------+
 *
 */
 
static size_t bios_size;
 
static struct region_device shadow_dev;
static struct xlate_region_device real_dev;
static struct xlate_window real_dev_window;
 
static void bios_mmap_init(void)
{
        size_t size, start, bios_mapped_size;
        uintptr_t base;
 
        size = bios_size;
 
        /* If bios_size is initialized, then bail out. */
        if (size != 0)
                return;
        start = fast_spi_get_bios_region(&size);
 
        /* BIOS region is mapped right below 4G. */
        base = 4ULL * GiB - size;
 
        /*
         * The 256 KiB right below 4G are decoded by readonly SRAM,
         * not boot media.
         */
        bios_mapped_size = size - 256 * KiB;
 
        rdev_chain_mem(&shadow_dev, (void *)base, bios_mapped_size);
 
        xlate_window_init(&real_dev_window, &shadow_dev, start, bios_mapped_size);
        xlate_region_device_ro_init(&real_dev, 1, &real_dev_window, CONFIG_ROM_SIZE);
 
        bios_size = size;
 
        /* Check that the CBFS lies within the memory mapped area. It's too
           easy to forget the SRAM mapping when crafting an FMAP file. */
        struct region cbfs_region;
        if (!fmap_locate_area("COREBOOT", &cbfs_region) &&
            !region_is_subregion(&real_dev_window.sub_region, &cbfs_region))
                printk(BIOS_CRIT,
                       "ERROR: CBFS @ %zx size %zx exceeds mem-mapped area @ %zx size %zx\n",
                       region_offset(&cbfs_region), region_sz(&cbfs_region),
                       start, bios_mapped_size);
}
 
const struct region_device *boot_device_ro(void)
{
        bios_mmap_init();
 
        return &real_dev.rdev;
}
 
uint32_t spi_flash_get_mmap_windows(struct flash_mmap_window *table)
{
        bios_mmap_init();
 
        table->flash_base = region_offset(&real_dev_window.sub_region);
        table->host_base = (uintptr_t)rdev_mmap_full(&shadow_dev);
        table->size = region_sz(&real_dev_window.sub_region);
 
        return 1;
}