[patch 51/57] ACPI: Ingore the RESET_REG_SUP bit when using ACPIreset mechanism

[Greg KH]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Zhao Yakui <yakui.zhao@xxxxxxxxx>

Subject: [patch 51/57] ACPI: Ingore the RESET_REG_SUP bit when using ACPI reset mechanism

commit 8fd145917fb62368a9b80db59562c20576238f5a upstream

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@xxxxxxxxx>
Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
Cc: Chuck Ebbert <cebbert@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 drivers/acpi/reboot.c |   25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

--- 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;

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