Message-ID: <cf19ac63-c758-45d1-90c3-fe09f5567c64@google.com>
Date: Wed, 14 Jan 2026 18:52:21 -0800
From: Amit Sunil Dhamne <amitsd@...gle.com>
To: André Draszik <andre.draszik@...aro.org>,
 Sebastian Reichel <sre@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Lee Jones <lee@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Badhri Jagan Sridharan <badhri@...gle.com>,
 Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
 Peter Griffin <peter.griffin@...aro.org>,
 Tudor Ambarus <tudor.ambarus@...aro.org>,
 Alim Akhtar <alim.akhtar@...sung.com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-usb@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org,
 RD Babiera <rdbabiera@...gle.com>, Kyle Tso <kyletso@...gle.com>
Subject: Re: [PATCH v3 4/5] power: supply: max77759: add charger driver


On 1/14/26 2:20 AM, André Draszik wrote:
> On Tue, 2026-01-13 at 16:47 -0800, Amit Sunil Dhamne wrote:
>> Hi Andre',
>>
>> On 1/13/26 2:02 AM, André Draszik wrote:
>>> Hi Amit,
>>>
>>> On Mon, 2026-01-12 at 11:37 -0800, Amit Sunil Dhamne wrote:
>>>> Hi Andre',
>>>>
>>>> On 1/12/26 5:47 AM, André Draszik wrote:
>>>>> Hi Amit,
>>>>>
>>>>> On Tue, 2026-01-06 at 17:14 -0800, Amit Sunil Dhamne wrote:
>>>>>> On 1/6/26 3:41 PM, Amit Sunil Dhamne wrote:
>>>>>>> Hi Andre',
>>>>>>>
>>>>>>> On 1/5/26 9:32 AM, André Draszik wrote:
>>>>>>>> Hi Amit,
>>>>>>>>
>>>>>>>> I haven't done a full review, but a few things caught my eye.
>>>>>>>>
>>>>>>>> On Sat, 2025-12-27 at 00:04 +0000, Amit Sunil Dhamne via B4 Relay wrote:
>>>>>>>>> diff --git a/drivers/power/supply/Makefile
>>>>>>>>> b/drivers/power/supply/Makefile
>>>>>>>>> index 4b79d5abc49a..6af905875ad5 100644
>>>>>>>>> --- a/drivers/power/supply/Makefile
>>>>>>>>> +++ b/drivers/power/supply/Makefile
>>>>>>>>> [...]
>>>>>>>>> +
>>>>>>>>> +static irqreturn_t irq_handler(int irq, void *data)
>>>>>>>>> +{
>>>>>>>>> +    struct max77759_charger *chg = data;
>>>>>>>>> +    struct device *dev = chg->dev;
>>>>>>>>> +    u32 chgint_ok;
>>>>>>>>> +    int i;
>>>>>>>>> +
>>>>>>>>> +    regmap_read(chg->regmap, MAX77759_CHGR_REG_CHG_INT_OK,
>>>>>>>>> &chgint_ok);
>>>>>>>> You might want to check the return value and return IRQ_NONE if it
>>>>>>>> didn't
>>>>>>>> work?
>>>>>>>>
>>>>>>>>> +
>>>>>>>>> +    for (i = 0; i < ARRAY_SIZE(irqs); i++) {
>>>>>>>>> +        if (irqs[i] == irq)
>>>>>>>>> +            break;
>>>>>>>>> +    }
>>>>>>>>> +
>>>>>>>>> +    switch (i) {
>>>>>>>>> +    case AICL:
>>>>>>>>> +        dev_dbg(dev, "AICL mode: %s",
>>>>>>>>> +            str_no_yes(chgint_ok & MAX77759_CHGR_REG_CHG_INT_AICL));
>>>>>>>>> +        break;
>>>>>>>>> +    case CHGIN:
>>>>>>>>> +        dev_dbg(dev, "CHGIN input valid: %s",
>>>>>>>>> +            str_yes_no(chgint_ok & MAX77759_CHGR_REG_CHG_INT_CHGIN));
>>>>>>>>> +        break;
>>>>>>>>> +    case CHG:
>>>>>>>>> +        dev_dbg(dev, "CHG status okay/off: %s",
>>>>>>>>> +            str_yes_no(chgint_ok & MAX77759_CHGR_REG_CHG_INT_CHG));
>>>>>>>>> +        break;
>>>>>>>>> +    case INLIM:
>>>>>>>>> +        dev_dbg(dev, "Current Limit reached: %s",
>>>>>>>>> +            str_no_yes(chgint_ok & MAX77759_CHGR_REG_CHG_INT_INLIM));
>>>>>>>>> +        break;
>>>>>>>>> +    case BAT_OILO:
>>>>>>>>> +        dev_dbg(dev, "Battery over-current threshold crossed");
>>>>>>>>> +        break;
>>>>>>>>> +    case CHG_STA_CC:
>>>>>>>>> +        dev_dbg(dev, "Charger reached CC stage");
>>>>>>>>> +        break;
>>>>>>>>> +    case CHG_STA_CV:
>>>>>>>>> +        dev_dbg(dev, "Charger reached CV stage");
>>>>>>>>> +        break;
>>>>>>>>> +    case CHG_STA_TO:
>>>>>>>>> +        dev_dbg(dev, "Charger reached TO stage");
>>>>>>>>> +        break;
>>>>>>>>> +    case CHG_STA_DONE:
>>>>>>>>> +        dev_dbg(dev, "Charger reached TO stage");
>>>>>>>>> +        break;
>>>>>>>> Are the above debug messages really all needed?
>>>>>> I forgot to respond to this comment in my previous email.
>>>>>>
>>>>>> I think we can keep AICL, BAT_OILO, INLIM. They're either special
>>>>>> conditions (AICL) or faulty conditions (like BAT_OILO) and we can in
>>>>>> fact keep them at dev_info level. Rest can be removed and a
>>>>>> power_supply_changed() is sufficient.
>>>>>>
>>>>>> Let me know what you think?
>>>>> I don't think dev_info() in an interrupt handler is appropriate. At
>>>>> least it should be ratelimited.
>>>>>
>>>>> If it's something special / unexpected that needs attention, having
>>>>> a dev_dbg() message only will usually not be visible to anybody.
>>>> I agree. I can change the prints to dev_info_ratelimited for the stuff
>>>> we care about.
>>> If it's an erroneous condition, maybe warn or even err are more appropriate?
>>>
>>> But then, what is the expectation upon the user observing these messages?
>>> What can or should they do? Who is going to look at these and can do
>>> something sensible based on them?
>> The logging will help in postmortem analysis which may or may not
>> possible with just publishing uevents to userspace hoping that they log
>> the psy properties. Illustrating a situation:
>>
>> 1. Over current situation happened where the Battery to System current
>> exceeds the BAT_OILO threshold. This would also generate an interrupt.
>>
>> 2. The MAX77759 takes protective measures if the condition lasts for a
>> certain specified time and reset. Resetting will cause Vsys to collapse
>> to 0 if the system is only battery powered.
>>
>> 3. It'd be better that the BAT_OILO interrupt is logged in dmesg,
>> instead of just delegating it to user space as user can debug this
>> condition by looking at last_kmsg or pstore.
>>
>> 4. This signal can help the user debug conditions such as moisture (this
>> signal + contaminant detection) or indicative of a mechanical failure.
>>
>> I do agree though that this is a hypothetical or very rare situation and
>> if you have a strong opinion against this I am okay with removing the
>> prints completely.
> Thanks for details. OK, they sound useful in this case, but should still
> be warn, not dbg.

Sounds good, will fix.


>>
>>> Also, I just noticed there is a max77705 charger driver. It seems quite
>>> similar to this one, maybe it can be leveraged / extended?
>> Thanks for the feedback. I reviewed the max77705 charger driver. .
>>
>> Here is a breakdown of why I believe a separate driver may be a better
>> approach:
> [...]
>
> Thanks for the analysis, I agree with your conclusion. Mainly I noticed that
> as part of AICL interrupt handling that driver does a bit of work, while here
> we don't. I am wondering if that is applicable here is well.

I double-checked the downstream drivers and datasheet. There exists no 
issue or WAR for max77759. Also, in case of max77759, the current 
limiting will be driven by the hardware and there's no need for software 
intervention. In case of max77705, the driver is explicitly reducing the 
current limit (in max77705_aicl_irq()), implying that hardware is just 
notifying the software to limit current due to (say) poor quality power 
source.


BR,

Amit

>
> Cheers,
> Andre'

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