The patch titled
Subject: drivers/rtc/rtc-rk808.c: fix rtc time reading issue
has been added to the -mm tree. Its filename is
rtc-rk808-fix-the-rtc-time-reading-issue.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/rtc-rk808-fix-the-rtc-time-reading-issue.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/rtc-rk808-fix-the-rtc-time-reading-issue.patch
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------------------------------------------------------
From: Chris Zhong <zyw@xxxxxxxxxxxxxx>
Subject: drivers/rtc/rtc-rk808.c: fix rtc time reading issue
After we set the GET_TIME bit, the rtc time can't be read immediately. We
should wait up to 31.25 us, about one cycle of 32khz. Otherwise reading
RTC time will return a old time. If we clear the GET_TIME bit after
setting, the time of i2c transfer is certainly more than 31.25us.
Doug said:
: I think we are safe. At 400kHz (the max speed of this part) each bit can
: be transferred no faster than 2.5us. In order to do a valid i2c
: transaction we need to _at least_ write the address of the device and the
: data onto the bus, which is 16 bits. 16 * 2.5us = 40us. That's above the
: 31.25us
Signed-off-by: Chris Zhong <zyw@xxxxxxxxxxxxxx>
Reviewed-by: Doug Anderson <dianders@xxxxxxxxxxxx>
Cc: Sonny Rao <sonnyrao@xxxxxxxxxxxx>
Cc: Heiko Stübner <heiko@xxxxxxxxx>
Cc: Alessandro Zummo <a.zummo@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/rtc/rtc-rk808.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff -puN drivers/rtc/rtc-rk808.c~rtc-rk808-fix-the-rtc-time-reading-issue drivers/rtc/rtc-rk808.c
--- a/drivers/rtc/rtc-rk808.c~rtc-rk808-fix-the-rtc-time-reading-issue
+++ a/drivers/rtc/rtc-rk808.c
@@ -67,15 +67,20 @@ static int rk808_rtc_readtime(struct dev
/* Force an update of the shadowed registers right now */
ret = regmap_update_bits(rk808->regmap, RK808_RTC_CTRL_REG,
BIT_RTC_CTRL_REG_RTC_GET_TIME,
- 0);
+ BIT_RTC_CTRL_REG_RTC_GET_TIME);
if (ret) {
dev_err(dev, "Failed to update bits rtc_ctrl: %d\n", ret);
return ret;
}
+ /* After we set the GET_TIME bit, the rtc time couldn't be read
+ * immediately, we should wait up to 31.25 us, about one cycle of
+ * 32khz. If we clear the GET_TIME bit here, the time of i2c transfer
+ * certainly more than 31.25us.
+ */
ret = regmap_update_bits(rk808->regmap, RK808_RTC_CTRL_REG,
BIT_RTC_CTRL_REG_RTC_GET_TIME,
- BIT_RTC_CTRL_REG_RTC_GET_TIME);
+ 0);
if (ret) {
dev_err(dev, "Failed to update bits rtc_ctrl: %d\n", ret);
return ret;
_
Patches currently in -mm which might be from zyw@xxxxxxxxxxxxxx are
rtc-rk808-fix-the-rtc-time-reading-issue.patch
rtc-rk808-fix-the-rtc-time-reading-issue-fix.patch
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