From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752577AbbANCnn (ORCPT ); Tue, 13 Jan 2015 21:43:43 -0500 Received: from mail-pa0-f50.google.com ([209.85.220.50]:43148 "EHLO mail-pa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750921AbbANCnm (ORCPT ); Tue, 13 Jan 2015 21:43:42 -0500 From: Chris Zhong To: akpm@linux-foundation.org Cc: dianders@chromium.org, heiko@sntech.de, linux-rockchip@lists.infradead.org, Chris Zhong , Alessandro Zummo , rtc-linux@googlegroups.com, linux-kernel@vger.kernel.org Subject: [PATCH] RTC: RK808: fix the rtc time reading issue Date: Wed, 14 Jan 2015 10:43:32 +0800 Message-Id: <1421203412-5159-1-git-send-email-zyw@rock-chips.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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