x86: apci: Change PM1_CNT register access to RMW

In enter_acpi_mode() PM1_CNT register is changed to PM1_CNT_SCI_EN
directly without preserving its previous value. Update to change
the register access to read-modify-write (RMW).

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Stefan Roese <sr@denx.de>

diff --git a/arch/x86/lib/acpi_table.c b/arch/x86/lib/acpi_table.c
index f118345..8be8120 100644 (file)
--- a/arch/x86/lib/acpi_table.c
+++ b/arch/x86/lib/acpi_table.c
@@ -306,6 +306,8 @@ static void acpi_create_mcfg(struct acpi_mcfg *mcfg)
 
 static void enter_acpi_mode(int pm1_cnt)
 {
+       u16 val = inw(pm1_cnt);
+
        /*
         * PM1_CNT register bit0 selects the power management event to be
         * either an SCI or SMI interrupt. When this bit is set, then power
@@ -320,7 +322,7 @@ static void enter_acpi_mode(int pm1_cnt)
         * system, and expose ourselves to OSPM as working under ACPI mode
         * already, turn this bit on.
         */
-       outw(PM1_CNT_SCI_EN, pm1_cnt);
+       outw(val | PM1_CNT_SCI_EN, pm1_cnt);
 }
 
 /*