[PATCH] rtc-ds1302: handle write protection
From: Sergey Yanovich
Date: Mon May 20 2013 - 19:06:31 EST
This chip has a control register and can prevent altering saved clock.
Without this patch we could have:
----8<----
(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
----8<----
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@xxxxxxxxx>
# Changes to be committed:
---
changes for v2:
- do enable/disable around set_time() instead of in probe()/remove()
drivers/rtc/rtc-ds1302.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/rtc/rtc-ds1302.c b/drivers/rtc/rtc-ds1302.c
index 7533b72..07e8d79 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;
}
--
1.7.10.4
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