ACPICA: clear fields reserved before FADT r3

Linux-2.6.21 stopped booting on a P4/HT because Linux
wrote the FADT.CST_CNT value to the SMI_CMD.
Apparently this stumbled over some SMM instability,
such as confusing SMM when invoking it from cpu1.

Linux did this because even though the r2 FADT reserves
the CST_CNT field, this BIOS set that field and Linux
used it.

Turns out that up through 2.6.20 we explicitly cleared
cst_control for r2 FADTs.  So here we go back to doing that,
plus also clear some additional fields that are reserved
until FADT r3.

http://bugzilla.kernel.org/show_bug.cgi?id=8346

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/tables/tbfadt.c

@@ -347,6 +347,18 @@ static void acpi_tb_convert_fadt(void)
 		acpi_gbl_xpm1b_enable.space_id = acpi_gbl_FADT.xpm1a_event_block.space_id;
 
 	}
+
+	/*
+	 * For ACPI 1.0 FADTs, ensure that reserved fields (which should be zero)
+	 * are indeed zero. This will workaround BIOSs that inadvertently placed
+	 * values in these fields.
+	 */
+	if (acpi_gbl_FADT.header.revision < 3) {
+		acpi_gbl_FADT.preferred_profile = 0;
+		acpi_gbl_FADT.pstate_control = 0;
+		acpi_gbl_FADT.cst_control = 0;
+		acpi_gbl_FADT.boot_flags = 0;
+	}
 }
 
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