[merged] rtc-rk808-fix-the-rtc-time-reading-issue.patch removed from -mm tree

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The patch titled
     Subject: drivers/rtc/rtc-rk808.c: fix rtc time reading issue
has been removed from the -mm tree.  Its filename was
     rtc-rk808-fix-the-rtc-time-reading-issue.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
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

[akpm@xxxxxxxxxxxxxxxxxxxx: tweak comment per review discussion]
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 |   10 ++++++++--
 1 file changed, 8 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 +67,21 @@ 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 can't be read
+	 * immediately. So 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: 16 * 2.5us at 400kHz bus frequency.
+	 */
 	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

origin.patch
linux-next.patch

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