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;