ANDROID: rtc-palmas: correct for bcd year

Replace bcd2bin and bin2bcd with one that maps years 1970 to 2129
in a pattern that works with the underlying hardware.

The only transition that does not work correctly for this rtc clock
is the transition from 2099 to 2100, it proceeds to 2000. The rtc
clock retains and transitions the year correctly in all other
circumstances.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 26346842
Change-Id: Ie527700190b1ae4b4bc3c12279d875aa5985b168

drivers/rtc/rtc-palmas.c

@@ -45,6 +45,42 @@ struct palmas_rtc {
 /* Total number of RTC registers needed to set time*/
 #define PALMAS_NUM_TIME_REGS	(PALMAS_YEARS_REG - PALMAS_SECONDS_REG + 1)
 
+/*
+ * Special bin2bcd mapping to deal with bcd storage of year.
+ *
+ *   0-69                -> 0xD0
+ *  70-99  (1970 - 1999) -> 0xD0 - 0xF9 (correctly rolls to 0x00)
+ * 100-199 (2000 - 2099) -> 0x00 - 0x99 (does not roll to 0xA0 :-( )
+ * 200-229 (2100 - 2129) -> 0xA0 - 0xC9 (really for completeness)
+ * 230-                  -> 0xC9
+ *
+ * Confirmed: the only transition that does not work correctly for this rtc
+ * clock is the transition from 2099 to 2100, it proceeds to 2000. We will
+ * accept this issue since the clock retains and transitions the year correctly
+ * in all other conditions.
+ */
+static unsigned char year_bin2bcd(int val)
+{
+	if (val < 70)
+		return 0xD0;
+	if (val < 100)
+		return bin2bcd(val - 20) | 0x80; /* KISS leverage of bin2bcd */
+	if (val >= 230)
+		return 0xC9;
+	if (val >= 200)
+		return bin2bcd(val - 180) | 0x80;
+	return bin2bcd(val - 100);
+}
+
+static int year_bcd2bin(unsigned char val)
+{
+	if (val >= 0xD0)
+		return bcd2bin(val & 0x7F) + 20;
+	if (val >= 0xA0)
+		return bcd2bin(val & 0x7F) + 180;
+	return bcd2bin(val) + 100;
+}
+
 static int palmas_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
 	unsigned char rtc_data[PALMAS_NUM_TIME_REGS];
@@ -71,7 +107,7 @@ static int palmas_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	tm->tm_hour = bcd2bin(rtc_data[2]);
 	tm->tm_mday = bcd2bin(rtc_data[3]);
 	tm->tm_mon = bcd2bin(rtc_data[4]) - 1;
-	tm->tm_year = bcd2bin(rtc_data[5]) + 100;
+	tm->tm_year = year_bcd2bin(rtc_data[5]);
 
 	return ret;
 }
@@ -87,7 +123,7 @@ static int palmas_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	rtc_data[2] = bin2bcd(tm->tm_hour);
 	rtc_data[3] = bin2bcd(tm->tm_mday);
 	rtc_data[4] = bin2bcd(tm->tm_mon + 1);
-	rtc_data[5] = bin2bcd(tm->tm_year - 100);
+	rtc_data[5] = year_bin2bcd(tm->tm_year);
 
 	/* Stop RTC while updating the RTC time registers */
 	ret = palmas_update_bits(palmas, PALMAS_RTC_BASE, PALMAS_RTC_CTRL_REG,
@@ -142,7 +178,7 @@ static int palmas_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
 	alm->time.tm_hour = bcd2bin(alarm_data[2]);
 	alm->time.tm_mday = bcd2bin(alarm_data[3]);
 	alm->time.tm_mon = bcd2bin(alarm_data[4]) - 1;
-	alm->time.tm_year = bcd2bin(alarm_data[5]) + 100;
+	alm->time.tm_year = year_bcd2bin(alarm_data[5]);
 
 	ret = palmas_read(palmas, PALMAS_RTC_BASE, PALMAS_RTC_INTERRUPTS_REG,
 			&int_val);
@@ -173,7 +209,7 @@ static int palmas_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
 	alarm_data[2] = bin2bcd(alm->time.tm_hour);
 	alarm_data[3] = bin2bcd(alm->time.tm_mday);
 	alarm_data[4] = bin2bcd(alm->time.tm_mon + 1);
-	alarm_data[5] = bin2bcd(alm->time.tm_year - 100);
+	alarm_data[5] = year_bin2bcd(alm->time.tm_year);
 
 	ret = palmas_bulk_write(palmas, PALMAS_RTC_BASE,
 		PALMAS_ALARM_SECONDS_REG, alarm_data, PALMAS_NUM_TIME_REGS);