linux/drivers/acpi/reboot.c
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   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
   9static 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
  27static 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
  34void 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}
  81