Re: [PATCH RFC 06/11] power: supply: max77693: Set charge current limits during init

[Artur Weber <aweber.kernel@gmail.com>]

On 31.05.2024 11:47, Krzysztof Kozlowski wrote:
> On 30/05/2024 10:55, Artur Weber wrote:
>> There are two charger current limit registers:
>>
>> - Fast charge current limit (which controls current going from the
>>    charger to the battery);
>> - CHGIN input current limit (which controls current going into the
>>    charger through the cable, and is managed by the CHARGER regulator).
>>
>> Add functions for setting both of the values, and set them to a
>> safe default value of 500mA at initialization.
>>
>> The default value for the fast charge current limit can be modified
>> by setting the maxim,fast-charge-current-microamp DT property; the
>> CHGIN input current limit will be set up later in the charger detection
>> mechanism.
>>
>> Signed-off-by: Artur Weber <aweber.kernel@gmail.com>
>> ---
>>   drivers/power/supply/max77693_charger.c | 45 +++++++++++++++++++++++++++++++++
>>   1 file changed, 45 insertions(+)
>>
>> diff --git a/drivers/power/supply/max77693_charger.c b/drivers/power/supply/max77693_charger.c
>> index 894c35b750b3..d59b1524b0a4 100644
>> --- a/drivers/power/supply/max77693_charger.c
>> +++ b/drivers/power/supply/max77693_charger.c
>> @@ -28,6 +28,7 @@ struct max77693_charger {
>>   	u32 min_system_volt;
>>   	u32 thermal_regulation_temp;
>>   	u32 batttery_overcurrent;
>> +	u32 fast_charge_current;
>>   	u32 charge_input_threshold_volt;
>>   };
>>   
>> @@ -591,6 +592,35 @@ static int max77693_set_batttery_overcurrent(struct max77693_charger *chg,
>>   			CHG_CNFG_12_B2SOVRC_MASK, data);
>>   }
>>   
>> +static int max77693_set_input_current_limit(struct max77693_charger *chg,
>> +		unsigned int uamp)
>> +{
>> +	dev_dbg(chg->dev, "CHGIN input current limit: %u\n", uamp);
> 
> That's quite useless debug. It duplicates
> max77693_set_fast_charge_current(). Just drop entire wrapper.

It doesn't duplicate max77693_set_fast_charge_current, they modify two
separate registers. Quote from the commit message:

> There are two charger current limit registers:
> 
> - Fast charge current limit (which controls current going from the
>  charger to the battery);
> - CHGIN input current limit (which controls current going into the
>   charger through the cable, and is managed by the CHARGER regulator).

max77693_set_fast_charge_current sets up the "fast charge current"
register (in CNFG_02, CHG_CNFG_02_CC). The CHARGER regulators sets the
CHGIN input current (in CNFG_09, CHG_CNFG_09_CHGIN_ILIM).

(Apparently the CHARGER regulator is supposed to handle the fast
charge current, but it does not; I wrote about this in the "CHARGER
regulator" section of the patchset description.)

>> +
>> +	return regulator_set_current_limit(chg->regu, (int)uamp, (int)uamp);
>> +}
>> +
>> +static int max77693_set_fast_charge_current(struct max77693_charger *chg,
>> +		unsigned int uamp)
>> +{
>> +	unsigned int data;
>> +
>> +	data = (uamp / 1000) * 10 / 333; /* 0.1A/3 steps */
>> +
>> +	if (data > CHG_CNFG_02_CC_MASK) {
>> +		dev_err(chg->dev, "Wrong value for fast charge current\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	data <<= CHG_CNFG_02_CC_SHIFT;
>> +
>> +	dev_dbg(chg->dev, "Fast charge current: %u (0x%x)\n", uamp, data);
>> +
>> +	return regmap_update_bits(chg->max77693->regmap,
>> +			MAX77693_CHG_REG_CHG_CNFG_02,
>> +			CHG_CNFG_02_CC_MASK, data);
> 
> I am surprised that you set current limit via regulator but actual
> charging current value here. I think both should go to regulator in such
> case.

As in, both fast charge current and input current should be set up by
the CHARGER regulator? Sure, sounds good to me.

I've noticed that on the original kernel, both of the values are
modified together too (only exception is that fast charge current would
be set to 0 when the cable was unplugged, but the input current stayed
at 500mA. This doesn't seem to affect anything, though.).

At one point I actually considered going the other way around - moving
all charger register handling into the charger driver, instead of having
it be a regulator. As far as I can tell, only some Samsung-submitted
charger drivers (max77693, max8997, max8998, max14577) use a regulator
to manage the charger current (if anything, some power supply drivers
expose an OTG/VBUS regulator, might be something for us to consider as
well...).

I see you wrote at least the max14577 and part of the max77693 driver;
out of curiosity, what's the benefit of doing it through a current
regulator (as opposed to adding set functions for the relevant
properties in the charger driver)? I've noticed the downstream driver
has a very similar pattern[1], I wonder if it's just a port of that or
if there's a more concrete reason.

Best regards
Artur

[1] https://github.com/gr8nole/android_kernel_samsung_smdk4x12/blob/lineage-14.1/drivers/regulator/max77693.c (everything related to MAX77693_CHARGER)