mips/malta,loongson2ef: use generic mc146818_get_time function

mc146818_get_cmos_time() is now mostly equivalent to mc146818_get_time()
from drivers/rtc/rtc-mc146818-lib.c, with the latter using a more
advanced algorithm (which checks the UIP bit in the CMOS). The Malta
and Loongson2ef platforms, the only users of mc146818_get_cmos_time()
have RTC devices that should be MC146818 compatible.

So, rewrite mc146818_get_cmos_time() in a way that uses
mc146818_get_time() and add CONFIG_RTC_MC146818_LIB as a dependency of
CONFIG_MIPS_MALTA and CONFIG_CPU_LOONGSON2EF.

The should be safe as:

- malta_defconfig already uses a standard RTC CMOS driver
  (CONFIG_RTC_DRV_CMOS=y). The Malta board has an Intel 82371EB (PIIX4E)
  south bridge with the CMOS RTC, so should work correctly with the
  modification,

- Loongson2e and 2f apparently use the VIA686B south bridge and the AMD
  CS5536 south bridge respectively (at least according to Kconfig). I
  have checked datasheets of both and these appear to be MC146818
  software compatible.

Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Author: matjon

arch/mips/Kconfig

@@ -563,6 +563,7 @@ config MIPS_MALTA
 	select MIPS_L1_CACHE_SHIFT_6
 	select MIPS_MSC
 	select PCI_GT64XXX_PCI0
+	select RTC_MC146818_LIB
 	select SMP_UP if SMP
 	select SWAP_IO_SPACE
 	select SYS_HAS_CPU_MIPS32_R1
@@ -1837,6 +1838,7 @@ config CPU_LOONGSON2EF
 	select CPU_SUPPORTS_64BIT_KERNEL
 	select CPU_SUPPORTS_HIGHMEM
 	select CPU_SUPPORTS_HUGEPAGES
+	select RTC_MC146818_LIB
 
 config CPU_LOONGSON32
 	bool

arch/mips/include/asm/mc146818-time.h

@@ -8,41 +8,21 @@
 #ifndef __ASM_MC146818_TIME_H
 #define __ASM_MC146818_TIME_H
 
-#include <linux/bcd.h>
 #include <linux/mc146818rtc.h>
 #include <linux/time.h>
 
+#ifdef CONFIG_RTC_MC146818_LIB
 static inline time64_t mc146818_get_cmos_time(void)
 {
-	unsigned int year, mon, day, hour, min, sec;
-	unsigned long flags;
+	struct rtc_time tm;
 
-	spin_lock_irqsave(&rtc_lock, flags);
-
-	do {
-		sec = CMOS_READ(RTC_SECONDS);
-		min = CMOS_READ(RTC_MINUTES);
-		hour = CMOS_READ(RTC_HOURS);
-		day = CMOS_READ(RTC_DAY_OF_MONTH);
-		mon = CMOS_READ(RTC_MONTH);
-		year = CMOS_READ(RTC_YEAR);
-	} while (sec != CMOS_READ(RTC_SECONDS));
-
-	if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
-		sec = bcd2bin(sec);
-		min = bcd2bin(min);
-		hour = bcd2bin(hour);
-		day = bcd2bin(day);
-		mon = bcd2bin(mon);
-		year = bcd2bin(year);
+	if (mc146818_get_time(&tm, 1000)) {
+		pr_err("Unable to read current time from RTC\n");
+		return 0;
 	}
-	spin_unlock_irqrestore(&rtc_lock, flags);
-	if (year < 70)
-		year += 2000;
-	else
-		year += 1900;
 
-	return mktime64(year, mon, day, hour, min, sec);
+	return rtc_tm_to_time64(&tm);
 }
+#endif /* CONFIG_RTC_MC146818_LIB */
 
 #endif /* __ASM_MC146818_TIME_H */