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From:   Valentin Caron <valentin.caron@foss.st.com>
To:     Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Alessandro Zummo <a.zummo@towertech.it>
CC:     Alexandre Torgue <alexandre.torgue@foss.st.com>,
        Antonio Borneo <antonio.borneo@foss.st.com>,
        Christophe Guibout <christophe.guibout@foss.st.com>,
        Gabriel Fernandez <gabriel.fernandez@foss.st.com>,
        <linux-rtc@vger.kernel.org>,
        <linux-stm32@st-md-mailman.stormreply.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>,
        Valentin Caron <valentin.caron@foss.st.com>
Subject: [PATCH v2 1/7] rtc: stm32: use the proper register sequence to read date/time
Date:   Wed, 5 Jul 2023 19:43:51 +0200
Message-ID: <20230705174357.353616-2-valentin.caron@foss.st.com>
In-Reply-To: <20230705174357.353616-1-valentin.caron@foss.st.com>
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From: Antonio Borneo <antonio.borneo@foss.st.com>

Date and time are read from two separate RTC registers.
To ensure consistency between the two registers, reading the time
register locks the values in the shadow date register until the
date register is read.
Thus, the whole date/time read requires reading the time register
first, followed by reading the date register.
If the reads are done in reversed order, the shadow date register
will remain locked until a future read operation. The future read
will read the former date value that could be already invalid.

Fix the read order of date/time registers in stm32_rtc_valid_alrm()

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
---
 drivers/rtc/rtc-stm32.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-stm32.c b/drivers/rtc/rtc-stm32.c
index 3d36e11cff80..abb77ad774a1 100644
--- a/drivers/rtc/rtc-stm32.c
+++ b/drivers/rtc/rtc-stm32.c
@@ -429,8 +429,8 @@ static int stm32_rtc_valid_alrm(struct stm32_rtc *rtc, struct rtc_time *tm)
 {
 	const struct stm32_rtc_registers *regs = &rtc->data->regs;
 	int cur_day, cur_mon, cur_year, cur_hour, cur_min, cur_sec;
-	unsigned int dr = readl_relaxed(rtc->base + regs->dr);
 	unsigned int tr = readl_relaxed(rtc->base + regs->tr);
+	unsigned int dr = readl_relaxed(rtc->base + regs->dr);
 
 	cur_day = (dr & STM32_RTC_DR_DATE) >> STM32_RTC_DR_DATE_SHIFT;
 	cur_mon = (dr & STM32_RTC_DR_MONTH) >> STM32_RTC_DR_MONTH_SHIFT;
-- 
2.25.1