drivers/acpi/reboot.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #define pr_fmt(fmt) "ACPI: " fmt
   4
   5 #include <linux/pci.h>
   6 #include <linux/acpi.h>
   7 #include <acpi/reboot.h>
   8 #include <linux/delay.h>
   9
  10 #ifdef CONFIG_PCI
  11 static void acpi_pci_reboot(struct acpi_generic_address *rr, u8 reset_value)
  12 {
  13         unsigned int devfn;
  14         struct pci_bus *bus0;
  15
  16         /* The reset register can only live on bus 0. */
  17         bus0 = pci_find_bus(0, 0);
  18         if (!bus0)
  19                 return;
  20         /* Form PCI device/function pair. */
  21         devfn = PCI_DEVFN((rr->address >> 32) & 0xffff,
  22                           (rr->address >> 16) & 0xffff);
  23         pr_debug("Resetting with ACPI PCI RESET_REG.\n");
  24         /* Write the value that resets us. */
  25         pci_bus_write_config_byte(bus0, devfn,
  26                         (rr->address & 0xffff), reset_value);
  27 }
  28 #else
  29 static inline void acpi_pci_reboot(struct acpi_generic_address *rr,
  30                                    u8 reset_value)
  31 {
  32         pr_warn_once("PCI configuration space access is not supported\n");
  33 }
  34 #endif
  35
  36 void acpi_reboot(void)
  37 {
  38         struct acpi_generic_address *rr;
  39         u8 reset_value;
  40
  41         if (acpi_disabled)
  42                 return;
  43
  44         rr = &acpi_gbl_FADT.reset_register;
  45
  46         /* ACPI reset register was only introduced with v2 of the FADT */
  47
  48         if (acpi_gbl_FADT.header.revision < 2)
  49                 return;
  50
  51         /* Is the reset register supported? The spec says we should be
  52          * checking the bit width and bit offset, but Windows ignores
  53          * these fields */
  54         if (!(acpi_gbl_FADT.flags & ACPI_FADT_RESET_REGISTER))
  55                 return;
  56
  57         reset_value = acpi_gbl_FADT.reset_value;
  58
  59         /* The reset register can only exist in I/O, Memory or PCI config space
  60          * on a device on bus 0. */
  61         switch (rr->space_id) {
  62         case ACPI_ADR_SPACE_PCI_CONFIG:
  63                 acpi_pci_reboot(rr, reset_value);
  64                 break;
  65
  66         case ACPI_ADR_SPACE_SYSTEM_MEMORY:
  67         case ACPI_ADR_SPACE_SYSTEM_IO:
  68                 pr_debug("ACPI MEMORY or I/O RESET_REG.\n");
  69                 acpi_reset();
  70                 break;
  71         }
  72
  73         /*
  74          * Some platforms do not shut down immediately after writing to the
  75          * ACPI reset register, and this results in racing with the
  76          * subsequent reboot mechanism.
  77          *
  78          * The 15ms delay has been found to be long enough for the system
  79          * to reboot on the affected platforms.
  80          */
  81         mdelay(15);
  82 }