linux-kernel - Re: [PATCH 1/4] power: supply: add support for max77759 fuel gauge

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Message-ID: <7d63c607-dbd7-4109-812a-3936074f231f@uclouvain.be>
Date: Wed, 4 Dec 2024 09:53:11 +0100
From: Thomas Antoine <t.antoine@...ouvain.be>
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>, Dimitri Fedrau <dima.fedrau@...il.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Peter Griffin <peter.griffin@...aro.org>,
 Alim Akhtar <alim.akhtar@...sung.com>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 1/4] power: supply: add support for max77759 fuel gauge

On 12/3/24 12:02, André Draszik wrote:
> On Tue, 2024-12-03 at 11:11 +0100, Thomas Antoine wrote:
>> On 12/3/24 10:31, André Draszik wrote:
>>> On Tue, 2024-12-03 at 10:08 +0100, Thomas Antoine wrote:
>>>> On 12/3/24 07:47, André Draszik wrote:
>>>>>> From: Thomas Antoine <t.antoine@...ouvain.be>
>>>>>>
> [...]
> 
>>>>>>  /*
>>>>>>   * Model Gauge M5 Algorithm output register
>>>>>>   * Volatile data (must not be cached)
>>>>>> @@ -369,6 +387,8 @@ static int max1720x_battery_get_property(struct
>>>>>> power_supply *psy,
>>>>>>                       val->strval = max17201_model;
>>>>>>               else if (reg_val == MAX172XX_DEV_NAME_TYPE_MAX17205)
>>>>>>                       val->strval = max17205_model;
>>>>>> +             else if (reg_val == MAX172XX_DEV_NAME_TYPE_MAX77759)
>>>>>> +                     val->strval = max77759_model;
>>>>>>               else
>>>>>
>>>>> This is a 16 bit register, and while yes, MAX172XX_DEV_NAME_TYPE_MASK only
>>>>> cares about the bottom 4 bits, the register is described as 'Firmware
>>>>> Version Information'.
>>>>>
>>>>> But maybe it's ok to do it like that, at least for now.
>>>>
>>>> I thought this method would be ok as long as there is no collision on
>>>> values. I hesitated to change the model evaluation method based on chip
>>>> model, where the max77759 would thus have an hard-coded value and the
>>>> max1720x would still evaluate the register value. I did not do it because
>>>> it led to a lot more changes for no difference.
>>>
>>> Downstream uses the upper bits for max77759:
>>> https://android.googlesource.com/kernel/google-modules/bms/+/refs/heads/android-gs-raviole-mainline/max_m5.h#135
>>>
>>> I don't know what the original max17201/5 report in this register
>>> for those bits, though. Given for max77759 this register returns
>>> the firmware version, I assume the lower bits can change.
>>
>> Based on this datasheet of the max1720x, the upper bits are the revision
>> and the four lower bits are device. So it could change.
>> https://www.analog.com/media/en/technical-documentation/data-sheets/MAX17201-MAX17215.pdf#MAX17201%20DS.indd%3A.213504%3A15892
>>
>> If the four lower bits are not always 0 for the max77759 then I guess it
>> is necessary to change this as it wouldn't work with all max77759.
> 
> Maybe the best way forward is to go by the compatible (from DT), and
> if max77759 to then print a warning if the upper bits are != 0x62 and
> != 0x63. And maybe even refuse to load in that case.

Will implement this for v2, thank you.

Best regards,
Thomas