ACPI: Ingore the RESET_REG_SUP bit when using ACPI reset mechanism

According to ACPI 3.0, FADT.flags.RESET_REG_SUP indicates
whether the ACPI reboot mechanism is supported.

However, some boxes have this bit clear, have 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.

Here we stop checking RESET_REG_SUP.
Instead, 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

http://bugzilla.kernel.org/show_bug.cgi?id=7299
http://bugzilla.kernel.org/show_bug.cgi?id=1148

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

diff --git a/drivers/acpi/reboot.c b/drivers/acpi/reboot.c
index a6b662c..755baf2 100644 (file)
--- 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;