drivers/acpi/reboot.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include <linux/pci.h>
   4 #include <linux/acpi.h>
   5 #include <acpi/reboot.h>
   6 #include <linux/delay.h>
   7
   8 #ifdef CONFIG_PCI
   9 static void acpi_pci_reboot(struct acpi_generic_address *rr, u8 reset_value)
  10 {
  11         unsigned int devfn;
  12         struct pci_bus *bus0;
  13
  14         /* The reset register can only live on bus 0. */
  15         bus0 = pci_find_bus(0, 0);
  16         if (!bus0)
  17                 return;
  18         /* Form PCI device/function pair. */
  19         devfn = PCI_DEVFN((rr->address >> 32) & 0xffff,
  20                           (rr->address >> 16) & 0xffff);
  21         pr_debug("Resetting with ACPI PCI RESET_REG.\n");
  22         /* Write the value that resets us. */
  23         pci_bus_write_config_byte(bus0, devfn,
  24                         (rr->address & 0xffff), reset_value);
  25 }
  26 #else
  27 static inline void acpi_pci_reboot(struct acpi_generic_address *rr,
  28                                    u8 reset_value)
  29 {
  30         pr_warn_once("PCI configuration space access is not supported\n");
  31 }
  32 #endif
  33
  34 void acpi_reboot(void)
  35 {
  36         struct acpi_generic_address *rr;
  37         u8 reset_value;
  38
  39         if (acpi_disabled)
  40                 return;
  41
  42         rr = &acpi_gbl_FADT.reset_register;
  43
  44         /* ACPI reset register was only introduced with v2 of the FADT */
  45
  46         if (acpi_gbl_FADT.header.revision < 2)
  47                 return;
  48
  49         /* Is the reset register supported? The spec says we should be
  50          * checking the bit width and bit offset, but Windows ignores
  51          * these fields */
  52         if (!(acpi_gbl_FADT.flags & ACPI_FADT_RESET_REGISTER))
  53                 return;
  54
  55         reset_value = acpi_gbl_FADT.reset_value;
  56
  57         /* The reset register can only exist in I/O, Memory or PCI config space
  58          * on a device on bus 0. */
  59         switch (rr->space_id) {
  60         case ACPI_ADR_SPACE_PCI_CONFIG:
  61                 acpi_pci_reboot(rr, reset_value);
  62                 break;
  63
  64         case ACPI_ADR_SPACE_SYSTEM_MEMORY:
  65         case ACPI_ADR_SPACE_SYSTEM_IO:
  66                 printk(KERN_DEBUG "ACPI MEMORY or I/O RESET_REG.\n");
  67                 acpi_reset();
  68                 break;
  69         }
  70
  71         /*
  72          * Some platforms do not shut down immediately after writing to the
  73          * ACPI reset register, and this results in racing with the
  74          * subsequent reboot mechanism.
  75          *
  76          * The 15ms delay has been found to be long enough for the system
  77          * to reboot on the affected platforms.
  78          */
  79         mdelay(15);
  80 }