rtc: m48t59: Use platform_data struct for year offset value

Instead of hard-coded values and ifdefs, store the year offset in the
platform_data struct.

Tested-by: Daniel Palmer <daniel@0x0f.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
Tested-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: Andreas Larsson <andreas@gaisler.com>
Link: https://lore.kernel.org/r/665c3526184a8d0c4a6373297d8e7d9a12591d8b.1731450735.git.fthain@linux-m68k.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Author: fthain

arch/sparc/kernel/time_32.c

@@ -255,6 +255,7 @@ static void mostek_write_byte(struct device *dev, u32 ofs, u8 val)
 static struct m48t59_plat_data m48t59_data = {
 	.read_byte = mostek_read_byte,
 	.write_byte = mostek_write_byte,
+	.yy_offset = 68,
 };
 
 /* resource is set at runtime */

arch/sparc/kernel/time_64.c

@@ -544,6 +544,7 @@ static void mostek_write_byte(struct device *dev, u32 ofs, u8 val)
 static struct m48t59_plat_data m48t59_data = {
 	.read_byte	= mostek_read_byte,
 	.write_byte	= mostek_write_byte,
+	.yy_offset	= 68,
 };
 
 static struct platform_device m48t59_rtc = {

drivers/rtc/rtc-m48t59.c

@@ -71,7 +71,7 @@ static int m48t59_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	/* Issue the READ command */
 	M48T59_SET_BITS(M48T59_CNTL_READ, M48T59_CNTL);
 
-	tm->tm_year	= bcd2bin(M48T59_READ(M48T59_YEAR));
+	tm->tm_year	= bcd2bin(M48T59_READ(M48T59_YEAR)) + pdata->yy_offset;
 	/* tm_mon is 0-11 */
 	tm->tm_mon	= bcd2bin(M48T59_READ(M48T59_MONTH)) - 1;
 	tm->tm_mday	= bcd2bin(M48T59_READ(M48T59_MDAY));
@@ -82,10 +82,6 @@ static int m48t59_rtc_read_time(struct device *dev, struct rtc_time *tm)
 		dev_dbg(dev, "Century bit is enabled\n");
 		tm->tm_year += 100;	/* one century */
 	}
-#ifdef CONFIG_SPARC
-	/* Sun SPARC machines count years since 1968 */
-	tm->tm_year += 68;
-#endif
 
 	tm->tm_wday	= bcd2bin(val & 0x07);
 	tm->tm_hour	= bcd2bin(M48T59_READ(M48T59_HOUR) & 0x3F);
@@ -106,12 +102,7 @@ static int m48t59_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	struct m48t59_private *m48t59 = dev_get_drvdata(dev);
 	unsigned long flags;
 	u8 val = 0;
-	int year = tm->tm_year;
-
-#ifdef CONFIG_SPARC
-	/* Sun SPARC machines count years since 1968 */
-	year -= 68;
-#endif
+	int year = tm->tm_year - pdata->yy_offset;
 
 	dev_dbg(dev, "RTC set time %04d-%02d-%02d %02d/%02d/%02d\n",
 		year + 1900, tm->tm_mon, tm->tm_mday,
@@ -162,11 +153,7 @@ static int m48t59_rtc_readalarm(struct device *dev, struct rtc_wkalrm *alrm)
 	/* Issue the READ command */
 	M48T59_SET_BITS(M48T59_CNTL_READ, M48T59_CNTL);
 
-	tm->tm_year = bcd2bin(M48T59_READ(M48T59_YEAR));
-#ifdef CONFIG_SPARC
-	/* Sun SPARC machines count years since 1968 */
-	tm->tm_year += 68;
-#endif
+	tm->tm_year = bcd2bin(M48T59_READ(M48T59_YEAR)) + pdata->yy_offset;
 	/* tm_mon is 0-11 */
 	tm->tm_mon = bcd2bin(M48T59_READ(M48T59_MONTH)) - 1;
 
@@ -197,12 +184,7 @@ static int m48t59_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
 	struct rtc_time *tm = &alrm->time;
 	u8 mday, hour, min, sec;
 	unsigned long flags;
-	int year = tm->tm_year;
-
-#ifdef CONFIG_SPARC
-	/* Sun SPARC machines count years since 1968 */
-	year -= 68;
-#endif
+	int year = tm->tm_year - pdata->yy_offset;
 
 	/* If no irq, we don't support ALARM */
 	if (m48t59->irq == NO_IRQ)

include/linux/rtc/m48t59.h

@@ -56,6 +56,9 @@ struct m48t59_plat_data {
 	void __iomem *ioaddr;
 	/* offset to RTC registers, automatically set according to the type */
 	unsigned int offset;
+
+	/* YY digits (in RTC) are offset, i.e. year is 1900 + yy_offset + YY */
+	int yy_offset;
 };
 
 #endif /* _LINUX_RTC_M48T59_H_ */