linux-kernel - Re: [PATCH] rtc: rv3028: Improve trickle charger logic

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Date:   Thu, 8 Jun 2023 12:35:17 +0200
From:   Andrej Picej <andrej.picej@...ik.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     a.zummo@...ertech.it, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org, upstream@...tec.de
Subject: Re: [PATCH] rtc: rv3028: Improve trickle charger logic

Hi Alexandre,

On 8. 06. 23 11:31, Alexandre Belloni wrote:
> Hello,
> 
> On 08/06/2023 11:04:46+0200, Andrej Picej wrote:
>> +	ret = regmap_read(rv3028->regmap, RV3028_BACKUP, &val_old);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	/* mask out only trickle charger bits */
>> +	val_old = val_old & (RV3028_BACKUP_TCE | RV3028_BACKUP_TCR_MASK);
>> +
>>   	/* setup trickle charger */
>> -	if (!device_property_read_u32(&client->dev, "trickle-resistor-ohms",
>> -				      &ohms)) {
>> +	if (device_property_read_u32(&client->dev, "trickle-resistor-ohms", &ohms)) {
>> +		/* disable the trickle charger */
>> +		val = 0;
> 
> You can't do that, this will break existing users that may set the
> trickle charger from their bootloader for example.

hmm...ok I understand that idea. I thought that might be a problem. I 
guess keeping default as it is has a higher priority.

What do you say if setting this property to 0 (or maybe -1) disabled the 
trickle charger?
So if users add:

trickle-resistor-ohms = <0>;
or
trickle-resistor-ohms = <(-1)>;

this would mean disable the trickle charger?

I know it is far from optimal, but this would solve both things:
* not braking existing implementation,
* users could disable the trickle charger.

What do you say.

Thanks for your review.

Best regards,
Andrej

> 
>> +	} else {
>>   		int i;
>>   
>>   		for (i = 0; i < ARRAY_SIZE(rv3028_trickle_resistors); i++)
>> @@ -947,15 +957,21 @@ static int rv3028_probe(struct i2c_client *client)
>>   				break;
>>   
>>   		if (i < ARRAY_SIZE(rv3028_trickle_resistors)) {
>> -			ret = rv3028_update_cfg(rv3028, RV3028_BACKUP, RV3028_BACKUP_TCE |
>> -						 RV3028_BACKUP_TCR_MASK, RV3028_BACKUP_TCE | i);
>> -			if (ret)
>> -				return ret;
>> +			/* enable the trickle charger and setup its resistor accordingly */
>> +			val = RV3028_BACKUP_TCE | i;
>>   		} else {
>>   			dev_warn(&client->dev, "invalid trickle resistor value\n");
>>   		}
>>   	}
>>   
>> +	/* only update EEPROM if changes are necessary */
>> +	if (val_old != val) {
>> +		ret = rv3028_update_cfg(rv3028, RV3028_BACKUP, RV3028_BACKUP_TCE |
>> +					RV3028_BACKUP_TCR_MASK, val);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>>   	ret = rtc_add_group(rv3028->rtc, &rv3028_attr_group);
>>   	if (ret)
>>   		return ret;
>> -- 
>> 2.25.1
>>
>