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

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Date:   Wed, 26 Oct 2022 17:17:26 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.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 Alexandre,

On 10/7/22 15:05, Sean Anderson wrote:
> 
> 
> On 10/7/22 2:57 PM, Alexandre Belloni wrote:
>> 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.
> 
> I think it's important to warn the user if the oscillator actually fails
> so they can e.g. replace the crystal. Additionally, this can help debug
> failed batteries, since you will see "Time data invalid" in the boot log.

Have you considered my reply?

I'd also like to note that 

drivers/rtc/rtc-ds1672.c
drivers/rtc/rtc-pcf*.c
drivers/rtc/rtc-rs5c*.c
drivers/rtc/rtc-sc27xx.c

all produce some kind of message if they detect a power loss or oscillator failure.

--Sean


>>> +			/*
>>> +			 * 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
>>> 
>>