linux-kernel - [PATCH] RTC: RK808: fix the rtc time reading issue

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Date:	Wed, 14 Jan 2015 10:43:32 +0800
From:	Chris Zhong <zyw@...k-chips.com>
To:	akpm@...ux-foundation.org
Cc:	dianders@...omium.org, heiko@...ech.de,
	linux-rockchip@...ts.infradead.org,
	Chris Zhong <zyw@...k-chips.com>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	rtc-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: [PATCH] RTC: RK808: fix the rtc time reading issue

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. Otherwise reading
RTC time will return a old time. If clear the GET_TIME bit after setting,
the time of i2c transfer certainly more than 31.25us.

Signed-off-by: Chris Zhong <zyw@...k-chips.com>

---

 drivers/rtc/rtc-rk808.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-rk808.c b/drivers/rtc/rtc-rk808.c
index df42257..8dae322 100644
--- a/drivers/rtc/rtc-rk808.c
+++ b/drivers/rtc/rtc-rk808.c
@@ -67,15 +67,20 @@ static int rk808_rtc_readtime(struct device *dev, struct rtc_time *tm)
 	/* 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;
-- 
1.9.1

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