linux-kernel - [PATCH 1/2] rtc: m48t59: Accommodate chips that lack a century bit

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Message-Id: <f9eedf61f64906006f57ac88bdc160e55bc40c8a.1727925802.git.fthain@linux-m68k.org>
Date: Thu, 03 Oct 2024 13:23:22 +1000
From: Finn Thain <fthain@...ux-m68k.org>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>,
    Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Daniel Palmer <daniel@...f.com>,
    Michael Pavone <pavone@...rodev.com>,
    linux-m68k@...ts.linux-m68k.org,
    linux-rtc@...r.kernel.org,
    linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] rtc: m48t59: Accommodate chips that lack a century bit

The m48t59 driver is needed by both SPARC and MVME systems. Linux on
MVME uses 1970 as "year zero" rather than 1968 that's used on SPARC.
Add support for the MVME convention. Otherwise, the RTC on non-SPARC
systems can only read and write dates between 1900 and 1999.

Tested-by: Daniel Palmer <daniel@...f.com>
Signed-off-by: Finn Thain <fthain@...ux-m68k.org>
---
 drivers/rtc/rtc-m48t59.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/rtc/rtc-m48t59.c b/drivers/rtc/rtc-m48t59.c
index f0f6b9b6daec..e2d882ea5c2f 100644
--- a/drivers/rtc/rtc-m48t59.c
+++ b/drivers/rtc/rtc-m48t59.c
@@ -57,6 +57,17 @@ m48t59_mem_readb(struct device *dev, u32 ofs)
 	return readb(m48t59->ioaddr+ofs);
 }
 
+/*
+ * Sun SPARC machines count years since 1968. MVME machines running Linux
+ * count years since 1970.
+ */
+
+#ifdef CONFIG_SPARC
+#define YEAR0 68
+#else
+#define YEAR0 70
+#endif
+
 /*
  * NOTE: M48T59 only uses BCD mode
  */
@@ -82,10 +93,7 @@ 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_year += YEAR0;
 
 	tm->tm_wday	= bcd2bin(val & 0x07);
 	tm->tm_hour	= bcd2bin(M48T59_READ(M48T59_HOUR) & 0x3F);
@@ -108,10 +116,7 @@ static int m48t59_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	u8 val = 0;
 	int year = tm->tm_year;
 
-#ifdef CONFIG_SPARC
-	/* Sun SPARC machines count years since 1968 */
-	year -= 68;
-#endif
+	year -= YEAR0;
 
 	dev_dbg(dev, "RTC set time %04d-%02d-%02d %02d/%02d/%02d\n",
 		year + 1900, tm->tm_mon, tm->tm_mday,
@@ -163,10 +168,7 @@ static int m48t59_rtc_readalarm(struct device *dev, struct rtc_wkalrm *alrm)
 	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 += YEAR0;
 	/* tm_mon is 0-11 */
 	tm->tm_mon = bcd2bin(M48T59_READ(M48T59_MONTH)) - 1;
 
@@ -199,10 +201,7 @@ static int m48t59_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
 	unsigned long flags;
 	int year = tm->tm_year;
 
-#ifdef CONFIG_SPARC
-	/* Sun SPARC machines count years since 1968 */
-	year -= 68;
-#endif
+	year -= YEAR0;
 
 	/* If no irq, we don't support ALARM */
 	if (m48t59->irq == NO_IRQ)
-- 
2.39.5