diff options
| -rw-r--r-- | drivers/acpi/reboot.c | 25 |
1 files changed, 22 insertions, 3 deletions
diff --git a/drivers/acpi/reboot.c b/drivers/acpi/reboot.c index a6b662c00b67..755baf2ca70a 100644 --- a/drivers/acpi/reboot.c +++ b/drivers/acpi/reboot.c @@ -15,9 +15,28 @@ void acpi_reboot(void) rr = &acpi_gbl_FADT.reset_register; - /* Is the reset register supported? */ - if (!(acpi_gbl_FADT.flags & ACPI_FADT_RESET_REGISTER) || - rr->bit_width != 8 || rr->bit_offset != 0) + /* + * 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; |