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

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Date:   Thu, 15 Jun 2023 08:06:29 +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

On 8. 06. 23 12:35, Andrej Picej wrote:
> 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.

Gentle ping. Would this be something you would consider?

Thanks,
Andrej

> 
> 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
>>>
>>