linux-kernel - [PATCH 3/3] rtc: rs5c348: report error when time is invalid

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Date:   Mon, 24 Sep 2018 17:05:09 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     linux-rtc@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Subject: [PATCH 3/3] rtc: rs5c348: report error when time is invalid

Instead of resetting the RTC to an bogus valid time, let userspace know
that the time is invalid when XSTP is set. Reset XSTP when setting the time
again.

Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
---
 drivers/rtc/rtc-rs5c348.c | 43 +++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 22 deletions(-)

diff --git a/drivers/rtc/rtc-rs5c348.c b/drivers/rtc/rtc-rs5c348.c
index 7b9c7dc5b309..6582be707bd0 100644
--- a/drivers/rtc/rtc-rs5c348.c
+++ b/drivers/rtc/rtc-rs5c348.c
@@ -66,6 +66,17 @@ rs5c348_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	u8 txbuf[5+7], *txp;
 	int ret;
 
+	ret = spi_w8r8(spi, RS5C348_CMD_R(RS5C348_REG_CTL2));
+	if (ret < 0)
+		return ret;
+	if (ret & RS5C348_BIT_XSTP) {
+		txbuf[0] = RS5C348_CMD_W(RS5C348_REG_CTL2);
+		txbuf[1] = 0;
+		ret = spi_write_then_read(spi, txbuf, 2, NULL, 0);
+		if (ret < 0)
+			return ret;
+	}
+
 	/* Transfer 5 bytes before writing SEC.  This gives 31us for carry. */
 	txp = txbuf;
 	txbuf[0] = RS5C348_CMD_R(RS5C348_REG_CTL2); /* cmd, ctl2 */
@@ -102,6 +113,16 @@ rs5c348_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	u8 txbuf[5], rxbuf[7];
 	int ret;
 
+	ret = spi_w8r8(spi, RS5C348_CMD_R(RS5C348_REG_CTL2));
+	if (ret < 0)
+		return ret;
+	if (ret & RS5C348_BIT_VDET)
+		dev_warn(&spi->dev, "voltage-low detected.\n");
+	if (ret & RS5C348_BIT_XSTP) {
+		dev_warn(&spi->dev, "oscillator-stop detected.\n");
+		return -EINVAL;
+	}
+
 	/* Transfer 5 byte befores reading SEC.  This gives 31us for carry. */
 	txbuf[0] = RS5C348_CMD_R(RS5C348_REG_CTL2); /* cmd, ctl2 */
 	txbuf[1] = 0;	/* dummy */
@@ -165,28 +186,6 @@ static int rs5c348_probe(struct spi_device *spi)
 	dev_info(&spi->dev, "spiclk %u KHz.\n",
 		 (spi->max_speed_hz + 500) / 1000);
 
-	/* turn RTC on if it was not on */
-	ret = spi_w8r8(spi, RS5C348_CMD_R(RS5C348_REG_CTL2));
-	if (ret < 0)
-		return ret;
-	if (ret & (RS5C348_BIT_XSTP | RS5C348_BIT_VDET)) {
-		u8 buf[2];
-		struct rtc_time tm;
-		if (ret & RS5C348_BIT_VDET)
-			dev_warn(&spi->dev, "voltage-low detected.\n");
-		if (ret & RS5C348_BIT_XSTP)
-			dev_warn(&spi->dev, "oscillator-stop detected.\n");
-		rtc_time_to_tm(0, &tm);	/* 1970/1/1 */
-		ret = rs5c348_rtc_set_time(&spi->dev, &tm);
-		if (ret < 0)
-			return ret;
-		buf[0] = RS5C348_CMD_W(RS5C348_REG_CTL2);
-		buf[1] = 0;
-		ret = spi_write_then_read(spi, buf, sizeof(buf), NULL, 0);
-		if (ret < 0)
-			return ret;
-	}
-
 	ret = spi_w8r8(spi, RS5C348_CMD_R(RS5C348_REG_CTL1));
 	if (ret < 0)
 		return ret;
-- 
2.19.0