// SPDX-License-Identifier: GPL-2.0

#define pr_fmt(fmt) "ACPI: " fmt

#include <linux/pci.h>
#include <linux/acpi.h>
#include <acpi/reboot.h>
#include <linux/delay.h>

#ifdef CONFIG_PCI
static void acpi_pci_reboot(struct acpi_generic_address *rr, u8 reset_value)
{
        unsigned int devfn;
        struct pci_bus *bus0;

        /* The reset register can only live on bus 0. */
        bus0 = pci_find_bus(0, 0);
        if (!bus0)
                return;
        /* Form PCI device/function pair. */
        devfn = PCI_DEVFN((rr->address >> 32) & 0xffff,
                          (rr->address >> 16) & 0xffff);
        pr_debug("Resetting with ACPI PCI RESET_REG.\n");
        /* Write the value that resets us. */
        pci_bus_write_config_byte(bus0, devfn,
                        (rr->address & 0xffff), reset_value);
}
#else
static inline void acpi_pci_reboot(struct acpi_generic_address *rr,
                                   u8 reset_value)
{
        pr_warn_once("PCI configuration space access is not supported\n");
}
#endif

void acpi_reboot(void)
{
        struct acpi_generic_address *rr;
        u8 reset_value;

        if (acpi_disabled)
                return;

        rr = &acpi_gbl_FADT.reset_register;

        /* ACPI reset register was only introduced with v2 of the FADT */

        if (acpi_gbl_FADT.header.revision < 2)
                return;

        /* Is the reset register supported? The spec says we should be
         * checking the bit width and bit offset, but Windows ignores
         * these fields */
        if (!(acpi_gbl_FADT.flags & ACPI_FADT_RESET_REGISTER))
                return;

        reset_value = acpi_gbl_FADT.reset_value;

        /* The reset register can only exist in I/O, Memory or PCI config space
         * on a device on bus 0. */
        switch (rr->space_id) {
        case ACPI_ADR_SPACE_PCI_CONFIG:
                acpi_pci_reboot(rr, reset_value);
                break;

        case ACPI_ADR_SPACE_SYSTEM_MEMORY:
        case ACPI_ADR_SPACE_SYSTEM_IO:
                pr_debug("ACPI MEMORY or I/O RESET_REG.\n");
                acpi_reset();
                break;
        }

        /*
         * Some platforms do not shut down immediately after writing to the
         * ACPI reset register, and this results in racing with the
         * subsequent reboot mechanism.
         *
         * The 15ms delay has been found to be long enough for the system
         * to reboot on the affected platforms.
         */
        mdelay(15);
}