src/drivers/pc80/rtc/mc146818rtc_boot.c

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2
   3 #include <console/console.h>
   4 #include <fallback.h>
   5 #include <pc80/mc146818rtc.h>
   6 #include <stdint.h>
   7
   8 #if  CONFIG_MAX_REBOOT_CNT > 15
   9 #error "CONFIG_MAX_REBOOT_CNT too high"
  10 #endif
  11
  12 static int boot_count(uint8_t rtc_byte)
  13 {
  14         return rtc_byte >> 4;
  15 }
  16
  17 static uint8_t increment_boot_count(uint8_t rtc_byte)
  18 {
  19         return rtc_byte + (1 << 4);
  20 }
  21
  22 static uint8_t boot_set_fallback(uint8_t rtc_byte)
  23 {
  24         return rtc_byte & ~RTC_BOOT_NORMAL;
  25 }
  26
  27 static int boot_use_normal(uint8_t rtc_byte)
  28 {
  29         return rtc_byte & RTC_BOOT_NORMAL;
  30 }
  31
  32 int do_normal_boot(void)
  33 {
  34         unsigned char byte;
  35
  36         if (cmos_error() || (CONFIG(USE_OPTION_TABLE) && !cmos_lb_cks_valid())) {
  37                 printk(BIOS_WARNING,
  38                        "Invalid CMOS checksum detected! Force fallback boot...\n");
  39                 byte = cmos_read(RTC_BOOT_BYTE);
  40                 byte &= boot_set_fallback(byte) & 0x0f;
  41                 byte |= 0xf << 4;
  42                 cmos_write(byte, RTC_BOOT_BYTE);
  43         }
  44
  45         /* The RTC_BOOT_BYTE is now o.k. see where to go. */
  46         byte = cmos_read(RTC_BOOT_BYTE);
  47
  48         /* Are we attempting to boot normally? */
  49         if (boot_use_normal(byte)) {
  50                 /* Are we already at the max count? */
  51                 if (boot_count(byte) < CONFIG_MAX_REBOOT_CNT)
  52                         byte = increment_boot_count(byte);
  53                 else
  54                         byte = boot_set_fallback(byte);
  55         }
  56
  57         /* Save the boot byte */
  58         cmos_write(byte, RTC_BOOT_BYTE);
  59
  60         /* Return selected code path for this boot attempt */
  61         return boot_use_normal(byte);
  62 }