linux-kernel - [PATCH] rtc: abx80x: Don't warn about oscillator failure after PoR

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Date:   Fri,  7 Oct 2022 12:37:12 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-rtc@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Sean Anderson <sean.anderson@...o.com>
Subject: [PATCH] rtc: abx80x: Don't warn about oscillator failure after PoR

According to the datasheet, the "oscillator failure" bit is set

> ...on a power on reset, when both the system and battery voltages have
> dropped below acceptable levels. It is also set if an Oscillator Failure
> occurs....

>From testing, this bit is also set if a software reset is initiated.

This bit has a confusing name; it really tells us whether the time data
is valid. We clear it when writing the time. If it is still set, that
means there is a persistent issue (such as an oscillator failure),
instead of a transient one (such as power loss).

Because there are several other reasons which might cause this bit
to be set (including booting for the first time or a battery failure),
do not warn about oscillator failures willy-nilly. This may cause system
integrators to waste time looking into the wrong line of investigation.

Signed-off-by: Sean Anderson <sean.anderson@...o.com>
---

 drivers/rtc/rtc-abx80x.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-abx80x.c b/drivers/rtc/rtc-abx80x.c
index 9b0138d07232..1eb752e4e39d 100644
--- a/drivers/rtc/rtc-abx80x.c
+++ b/drivers/rtc/rtc-abx80x.c
@@ -115,6 +115,7 @@ struct abx80x_priv {
 	struct rtc_device *rtc;
 	struct i2c_client *client;
 	struct watchdog_device wdog;
+	bool wrote_time;
 };
 
 static int abx80x_write_config_key(struct i2c_client *client, u8 key)
@@ -167,6 +168,7 @@ static int abx80x_enable_trickle_charger(struct i2c_client *client,
 static int abx80x_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
 	struct i2c_client *client = to_i2c_client(dev);
+	struct abx80x_priv *priv = i2c_get_clientdata(client);
 	unsigned char buf[8];
 	int err, flags, rc_mode = 0;
 
@@ -181,7 +183,18 @@ static int abx80x_rtc_read_time(struct device *dev, struct rtc_time *tm)
 			return flags;
 
 		if (flags & ABX8XX_OSS_OF) {
-			dev_err(dev, "Oscillator failure, data is invalid.\n");
+			/*
+			 * The OF bit can be set either because of a reset
+			 * (PoR/Software reset) or because of an oscillator
+			 * failure. Effectively, it indicates that the stored
+			 * time is invalid. When we write the time, we clear
+			 * this bit. If it stays set, then this indicates an
+			 * oscillator failure.
+			 */
+			if (priv->wrote_time)
+				dev_err(dev, "Oscillator failure\n");
+			else
+				dev_info(dev, "Time data invalid\n");
 			return -EINVAL;
 		}
 	}
@@ -207,6 +220,7 @@ static int abx80x_rtc_read_time(struct device *dev, struct rtc_time *tm)
 static int abx80x_rtc_set_time(struct device *dev, struct rtc_time *tm)
 {
 	struct i2c_client *client = to_i2c_client(dev);
+	struct abx80x_priv *priv = i2c_get_clientdata(client);
 	unsigned char buf[8];
 	int err, flags;
 
@@ -240,6 +254,7 @@ static int abx80x_rtc_set_time(struct device *dev, struct rtc_time *tm)
 		dev_err(&client->dev, "Unable to write oscillator status register\n");
 		return err;
 	}
+	priv->wrote_time = true;
 
 	return 0;
 }
-- 
2.35.1.1320.gc452695387.dirty