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
11static 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(domain: 0, busnr: 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(bus: bus0, devfn,
26 where: (rr->address & 0xffff), val: reset_value);
27}
28#else
29static 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
36void 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}
83