drivers/acpi/reboot.c

   1
   2 #include <linux/pci.h>
   3 #include <linux/acpi.h>
   4 #include <acpi/reboot.h>
   5
   6 void acpi_reboot(void)
   7 {
   8         struct acpi_generic_address *rr;
   9         struct pci_bus *bus0;
  10         u8 reset_value;
  11         unsigned int devfn;
  12
  13         if (acpi_disabled)
  14                 return;
  15
  16         rr = &acpi_gbl_FADT.reset_register;
  17
  18         /*
  19          * Is the ACPI reset register supported?
  20          *
  21          * According to ACPI 3.0, FADT.flags.RESET_REG_SUP indicates
  22          * whether the ACPI reset mechanism is supported.
  23          *
  24          * However, some boxes have this bit clear, yet a valid
  25          * ACPI_RESET_REG & RESET_VALUE, and ACPI reboot is the only
  26          * mechanism that works for them after S3.
  27          *
  28          * This suggests that other operating systems may not be checking
  29          * the RESET_REG_SUP bit, and are using other means to decide
  30          * whether to use the ACPI reboot mechanism or not.
  31          *
  32          * So when acpi reboot is requested,
  33          * only the reset_register is checked. If the following
  34          * conditions are met, it indicates that the reset register is supported.
  35          *      a. reset_register is not zero
  36          *      b. the access width is eight
  37          *      c. the bit_offset is zero
  38          */
  39         if (!(rr->address) || rr->bit_width != 8 || rr->bit_offset != 0)
  40                 return;
  41
  42         reset_value = acpi_gbl_FADT.reset_value;
  43
  44         /* The reset register can only exist in I/O, Memory or PCI config space
  45          * on a device on bus 0. */
  46         switch (rr->space_id) {
  47         case ACPI_ADR_SPACE_PCI_CONFIG:
  48                 /* The reset register can only live on bus 0. */
  49                 bus0 = pci_find_bus(0, 0);
  50                 if (!bus0)
  51                         return;
  52                 /* Form PCI device/function pair. */
  53                 devfn = PCI_DEVFN((rr->address >> 32) & 0xffff,
  54                                   (rr->address >> 16) & 0xffff);
  55                 printk(KERN_DEBUG "Resetting with ACPI PCI RESET_REG.");
  56                 /* Write the value that resets us. */
  57                 pci_bus_write_config_byte(bus0, devfn,
  58                                 (rr->address & 0xffff), reset_value);
  59                 break;
  60
  61         case ACPI_ADR_SPACE_SYSTEM_MEMORY:
  62         case ACPI_ADR_SPACE_SYSTEM_IO:
  63                 printk(KERN_DEBUG "ACPI MEMORY or I/O RESET_REG.\n");
  64                 acpi_hw_low_level_write(8, reset_value, rr);
  65                 break;
  66         }
  67         /* Wait ten seconds */
  68         acpi_os_stall(10000000);
  69 }