Change in coreboot[master]: libpayload: Improve rtc functions

[Patrick Georgi (Code Review)]

Patrick Georgi has submitted this change. ( https://review.coreboot.org/c/coreboot/+/18498 )

Change subject: libpayload: Improve rtc functions
......................................................................

libpayload: Improve rtc functions

On Lenovo T500 the RTC readings where wrong, as RTC has
different encodings, depending on the statusB register.

Support BCD vs binary RTC format and AM/PM vs 24h RTC format.

Fixes wrong date and time on Lenovo 500.

Change-Id: Id773c33e228973e190a7e14c3d11979678b1a619
Signed-off-by: Patrick Rudolph 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/18498
Tested-by: build bot (Jenkins) 
Reviewed-by: Nico Huber 
---
M payloads/libpayload/drivers/nvram.c
M payloads/libpayload/include/libpayload.h
2 files changed, 41 insertions(+), 9 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Nico Huber: Looks good to me, approved

diff --git a/payloads/libpayload/drivers/nvram.c b/payloads/libpayload/drivers/nvram.c
index a116d1b..34ee033 100644
--- a/payloads/libpayload/drivers/nvram.c
+++ b/payloads/libpayload/drivers/nvram.c
@@ -2,6 +2,7 @@
  * This file is part of the libpayload project.
  *
  * Copyright (C) 2008 Uwe Hermann 
+ * Copyright (C) 2017 Patrick Rudolph 
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -111,23 +112,51 @@
  */
 void rtc_read_clock(struct tm *time)
 {
+	u16 timeout = 10000;
+	u8 statusB;
+	u8 reg8;
+
    memset(time, 0, sizeof(*time));

-	while(nvram_updating());
+	while (nvram_updating())
+		if (!timeout--)
+			return;

-	time->tm_mon = bcd2dec(nvram_read(NVRAM_RTC_MONTH)) - 1;
-	time->tm_sec = bcd2dec(nvram_read(NVRAM_RTC_SECONDS));
-	time->tm_min = bcd2dec(nvram_read(NVRAM_RTC_MINUTES));
-	time->tm_mday = bcd2dec(nvram_read(NVRAM_RTC_DAY));
-	time->tm_hour = bcd2dec(nvram_read(NVRAM_RTC_HOURS));
+	statusB = nvram_read(NVRAM_RTC_STATUSB);
+
+	if (!(statusB & NVRAM_RTC_FORMAT_BINARY)) {
+		time->tm_mon = bcd2dec(nvram_read(NVRAM_RTC_MONTH)) - 1;
+		time->tm_sec = bcd2dec(nvram_read(NVRAM_RTC_SECONDS));
+		time->tm_min = bcd2dec(nvram_read(NVRAM_RTC_MINUTES));
+		time->tm_mday = bcd2dec(nvram_read(NVRAM_RTC_DAY));
+
+		if (!(statusB & NVRAM_RTC_FORMAT_24HOUR)) {
+			reg8 = nvram_read(NVRAM_RTC_HOURS);
+			time->tm_hour = bcd2dec(reg8 & 0x7f);
+			time->tm_hour += (reg8 & 0x80) ? 12 : 0;
+			time->tm_hour %= 24;
+		} else
+			time->tm_hour = bcd2dec(nvram_read(NVRAM_RTC_HOURS));
+		time->tm_year = bcd2dec(nvram_read(NVRAM_RTC_YEAR));
+	} else {
+		time->tm_mon = nvram_read(NVRAM_RTC_MONTH) - 1;
+		time->tm_sec = nvram_read(NVRAM_RTC_SECONDS);
+		time->tm_min = nvram_read(NVRAM_RTC_MINUTES);
+		time->tm_mday = nvram_read(NVRAM_RTC_DAY);
+		if (!(statusB & NVRAM_RTC_FORMAT_24HOUR)) {
+			reg8 = nvram_read(NVRAM_RTC_HOURS);
+			time->tm_hour = reg8 & 0x7f;
+			time->tm_hour += (reg8 & 0x80) ? 12 : 0;
+			time->tm_hour %= 24;
+		} else
+			time->tm_hour = nvram_read(NVRAM_RTC_HOURS);
+		time->tm_year = nvram_read(NVRAM_RTC_YEAR);
+	}

/* Instead of finding the century register,
       we just make an assumption that if the year value is
       less then 80, then it is 2000+
    */
-
-	time->tm_year = bcd2dec(nvram_read(NVRAM_RTC_YEAR));
-
    if (time->tm_year < 80)
    	time->tm_year += 100;
 }
diff --git a/payloads/libpayload/include/libpayload.h b/payloads/libpayload/include/libpayload.h
index 4b6a250..7496972 100644
--- a/payloads/libpayload/include/libpayload.h
+++ b/payloads/libpayload/include/libpayload.h
@@ -130,6 +130,9 @@
 #define NVRAM_RTC_YEAR           9      /**< RTC Year offset in CMOS */
 #define NVRAM_RTC_FREQ_SELECT    10     /**< RTC Update Status Register */
 #define  NVRAM_RTC_UIP           0x80
+#define NVRAM_RTC_STATUSB        11     /**< RTC Status Register B */
+#define  NVRAM_RTC_FORMAT_24HOUR 0x02
+#define  NVRAM_RTC_FORMAT_BINARY 0x04

/** Broken down time structure */
 struct tm {