drivers/rtc/rtc-ds1302.c: handle write protection (dfc657b1) · Commits · 戴 / test

This chip has a control register and can prevent altering saved clock. Without this patch we could have: (arm)root@pac14:~# date Tue May 21 03:08:27 MSK 2013 (arm)root@pac14:~# /etc/init.d/hwclock.sh show Tue May 21 11:13:58 2013 -0.067322 seconds (arm)root@pac14:~# /etc/init.d/hwclock.sh stop [info] Saving the system clock. [info] Hardware Clock updated to Tue May 21 03:09:01 MSK 2013. (arm)root@pac14:~# /etc/init.d/hwclock.sh show Tue May 21 11:14:15 2013 -0.624272 seconds The patch enables write access to rtc before the driver tries to write time and re-disables when time data is written. Signed-off-by:

Sergey Yanovich <ynvich@gmail.com> Acked-by:

Marc Zyngier <maz@misterjones.org> Cc: Alessandro Zummo <a.zummo@towertech.it> Cc: Sachin Kamat <sachin.kamat@linaro.org> Cc: Jingoo Han <jg1.han@samsung.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-ds1302.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -23,8 +23,12 @@
		#define RTC_CMD_READ 0x81 /* Read command */
		#define RTC_CMD_WRITE 0x80 /* Write command */

		#define RTC_CMD_WRITE_ENABLE 0x00 /* Write enable */
		#define RTC_CMD_WRITE_DISABLE 0x80 /* Write disable */

		#define RTC_ADDR_RAM0 0x20 /* Address of RAM0 */
		#define RTC_ADDR_TCR 0x08 /* Address of trickle charge register */
		#define RTC_ADDR_CTRL 0x07 /* Address of control register */
		#define RTC_ADDR_YEAR 0x06 /* Address of year register */
		#define RTC_ADDR_DAY 0x05 /* Address of day of week register */
		#define RTC_ADDR_MON 0x04 /* Address of month register */
		@@ -161,6 +165,7 @@ static int ds1302_rtc_read_time(struct device dev, struct rtc_time tm)

		static int ds1302_rtc_set_time(struct device dev, struct rtc_time tm)
		{
		ds1302_writebyte(RTC_ADDR_CTRL, RTC_CMD_WRITE_ENABLE);
		/* Stop RTC */
		ds1302_writebyte(RTC_ADDR_SEC, ds1302_readbyte(RTC_ADDR_SEC) \| 0x80);

		@@ -175,6 +180,8 @@ static int ds1302_rtc_set_time(struct device dev, struct rtc_time tm)
		/* Start RTC */
		ds1302_writebyte(RTC_ADDR_SEC, ds1302_readbyte(RTC_ADDR_SEC) & ~0x80);

		ds1302_writebyte(RTC_ADDR_CTRL, RTC_CMD_WRITE_DISABLE);

		return 0;
		}

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