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Commit dfc657b1 authored by Sergey Yanovich's avatar Sergey Yanovich Committed by Linus Torvalds
Browse files

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: default avatarSergey Yanovich <ynvich@gmail.com>
Acked-by: default avatarMarc 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 25d053cf

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;

}