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

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Date:   Fri, 7 Oct 2022 20:57:40 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Sean Anderson <sean.anderson@...o.com>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: abx80x: Don't warn about oscillator failure after
 PoR

Hi,

On 07/10/2022 12:37:12-0400, Sean Anderson wrote:
> 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");

Simply remove the line.

> +			/*
> +			 * 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
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com