drivers/acpi/reboot.c

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

void acpi_reboot(void)
{
	struct acpi_generic_address *rr;
	struct pci_bus *bus0;
	u8 reset_value;
	unsigned int devfn;

	if (acpi_disabled)
		return;

	rr = &acpi_gbl_FADT.reset_register;

	/*
	 * Is the ACPI reset register supported?
	 *
	 * According to ACPI 3.0, FADT.flags.RESET_REG_SUP indicates
	 * whether the ACPI reset mechanism is supported.
	 *
	 * However, some boxes have this bit clear, yet a valid
	 * ACPI_RESET_REG & RESET_VALUE, and ACPI reboot is the only
	 * mechanism that works for them after S3.
	 *
	 * This suggests that other operating systems may not be checking
	 * the RESET_REG_SUP bit, and are using other means to decide
	 * whether to use the ACPI reboot mechanism or not.
	 *
	 * So when acpi reboot is requested,
	 * only the reset_register is checked. If the following
	 * conditions are met, it indicates that the reset register is supported.
	 * 	a. reset_register is not zero
	 * 	b. the access width is eight
	 * 	c. the bit_offset is zero
	 */
	if (!(rr->address) || rr->bit_width != 8 || rr->bit_offset != 0)
		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:
		/* 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);
		printk(KERN_DEBUG "Resetting with ACPI PCI RESET_REG.");
		/* Write the value that resets us. */
		pci_bus_write_config_byte(bus0, devfn,
				(rr->address & 0xffff), reset_value);
		break;

	case ACPI_ADR_SPACE_SYSTEM_MEMORY:
	case ACPI_ADR_SPACE_SYSTEM_IO:
		printk(KERN_DEBUG "ACPI MEMORY or I/O RESET_REG.\n");
		acpi_hw_low_level_write(8, reset_value, rr);
		break;
	}
	/* Wait ten seconds */
	acpi_os_stall(10000000);
}