mc146818rtc: disable RTC before writing to nvram
In principle this isn't necessary. However there's a byte (or several)
outside the first 14 bytes that are part of the RTC, and require
locking (century/altCentury).
Since their location is mostly unknown, guard writes properly.
Change-Id: I847cd4efa92722e8504d29feaf7dbfa5c5244b4e
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/1868
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/src/include/pc80/mc146818rtc.h b/src/include/pc80/mc146818rtc.h
index 31322ea..ee1473b 100644
--- a/src/include/pc80/mc146818rtc.h
+++ b/src/include/pc80/mc146818rtc.h
@@ -110,7 +110,7 @@
return inb(RTC_BASE_PORT + offs + 1);
}
-static inline void cmos_write(unsigned char val, unsigned char addr)
+static inline void cmos_write_inner(unsigned char val, unsigned char addr)
{
int offs = 0;
if (addr >= 128) {
@@ -121,6 +121,35 @@
outb(val, RTC_BASE_PORT + offs + 1);
}
+static inline void cmos_write(unsigned char val, unsigned char addr)
+{
+ u8 control_state = cmos_read(RTC_CONTROL);
+ /* There are various places where RTC bits might be hiding,
+ * eg. the Century / AltCentury byte. So to be safe, disable
+ * RTC before changing any value.
+ */
+ if ((addr != RTC_CONTROL) && !(control_state & RTC_SET)) {
+ cmos_write_inner(control_state | RTC_SET, RTC_CONTROL);
+ }
+ cmos_write_inner(val, addr);
+ /* reset to prior configuration */
+ if ((addr != RTC_CONTROL) && !(control_state & RTC_SET)) {
+ cmos_write_inner(control_state, RTC_CONTROL);
+ }
+}
+
+static inline void cmos_disable_rtc(void)
+{
+ u8 control_state = cmos_read(RTC_CONTROL);
+ cmos_write(control_state | RTC_SET, RTC_CONTROL);
+}
+
+static inline void cmos_enable_rtc(void)
+{
+ u8 control_state = cmos_read(RTC_CONTROL);
+ cmos_write(control_state & ~RTC_SET, RTC_CONTROL);
+}
+
static inline u32 cmos_read32(u8 offset)
{
u32 value = 0;