Messages in this thread Patch in this message | | | Subject | [PATCH] rtc-ds1302: handle write protection | From | Sergey Yanovich <> | Date | Thu, 30 May 2013 20:04:48 +0400 |
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From f1cd048a066b249082752a96abce7d33a0cd4ea3 Mon Sep 17 00:00:00 2001 From: Sergey Yanovich <ynvich@gmail.com> Date: Tue, 21 May 2013 03:06:31 +0400 Subject: [PATCH] rtc-ds1302: handle write protection
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@gmail.com>
# 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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