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authorSergey Yanovich <ynvich@gmail.com>2013-07-03 15:07:46 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-03 16:07:59 -0700
commitdfc657b1330990213a3865aaef9d8af563ccad51 (patch)
tree412b7c83788b31c5448376c3663acd17390fa869 /drivers/rtc/rtc-ds1302.c
parent25d053cf1040e6430fff679854b3710edb0b7fee (diff)
drivers/rtc/rtc-ds1302.c: handle write protection
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>
Diffstat (limited to 'drivers/rtc/rtc-ds1302.c')
-rw-r--r--drivers/rtc/rtc-ds1302.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/rtc/rtc-ds1302.c b/drivers/rtc/rtc-ds1302.c
index 7533b723082d..07e8d79b4a09 100644
--- a/drivers/rtc/rtc-ds1302.c
+++ b/drivers/rtc/rtc-ds1302.c
@@ -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;
}