linux-kernel - Re: [PATCH] hwmon: (ina2xx) make regulator 'vs' support optional

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Message-ID: <47d24f17-c285-4e18-b0e7-fb6c6381f042@oss.nxp.com>
Date: Wed, 9 Apr 2025 10:03:02 +0300
From: Ciprian Marian Costea <ciprianmarian.costea@....nxp.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
 linux-kernel@...r.kernel.org, NXP S32 Linux <s32@....com>,
 imx@...ts.linux.dev, Christophe Lizzi <clizzi@...hat.com>,
 Alberto Ruiz <aruizrui@...hat.com>, Enric Balletbo <eballetb@...hat.com>,
 Eric Chanudet <echanude@...hat.com>, Florin Buica <florin.buica@....com>
Subject: Re: [PATCH] hwmon: (ina2xx) make regulator 'vs' support optional

On 4/8/2025 9:07 PM, Guenter Roeck wrote:
> On 4/4/25 01:36, Ciprian Marian Costea wrote:
>> On 4/3/2025 7:06 PM, Guenter Roeck wrote:
>>> On Thu, Apr 03, 2025 at 05:29:26PM +0300, Ciprian Marian Costea wrote:
>>>> On 4/3/2025 3:15 PM, Guenter Roeck wrote:
>>>>> On 4/3/25 03:15, Ciprian Costea wrote:
>>>>>> From: Ciprian Marian Costea <ciprianmarian.costea@....nxp.com>
>>>>>>
>>>>>> S32G2/S32G3 based boards which integrate the ina231 sensor do not 
>>>>>> have a
>>>>>> dedicated voltage regulator.
>>>>>>
>>>>>> Co-developed-by: Florin Buica <florin.buica@....com>
>>>>>> Signed-off-by: Florin Buica <florin.buica@....com>
>>>>>> Signed-off-by: Ciprian Marian Costea 
>>>>>> <ciprianmarian.costea@....nxp.com>
>>>>>> ---
>>>>>>    drivers/hwmon/ina2xx.c | 4 ++--
>>>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/hwmon/ina2xx.c b/drivers/hwmon/ina2xx.c
>>>>>> index 345fe7db9de9..ab4972f94a8c 100644
>>>>>> --- a/drivers/hwmon/ina2xx.c
>>>>>> +++ b/drivers/hwmon/ina2xx.c
>>>>>> @@ -959,8 +959,8 @@ static int ina2xx_probe(struct i2c_client 
>>>>>> *client)
>>>>>>            return PTR_ERR(data->regmap);
>>>>>>        }
>>>>>> -    ret = (dev, "vs");
>>>>>> -    if (ret)
>>>>>> +    ret = devm_regulator_get_enable_optional(dev, "vs");
>>>>>
>>>>> devm_regulator_get_enable() should provide a dummy regulator if 
>>>>> there is
>>>>> no explicit regulator. Why does this not work ?
>>>>>
>>>>>> +    if (ret < 0 && ret != -ENODEV)
>>>>>
>>>>> Why this added check ?
>>>>>
>>>>> I know it used to be necessary if regulator support is disabled,
>>>>> but that is no longer the case.
>>>>>
>>>>> Guenter
>>>>>
>>>>
>>>> Hello Guenter,
>>>>
>>>> I've just tested and devm_regulator_get_enable() does work as you've
>>>> described, providing a dummy regulator.
>>>>
>>>> But, according to the 'ti,ina2xx' binding [1] I see that the 
>>>> `vs-supply`
>>>> property is not required. Hence wouldn't it be correct for 
>>>> `vs-supply` to be
>>>> optional ? Using 'devm_regulator_get_enable_optional()'
>>>>
>>> Yes, but the reasoning you provided is different and suggested that the
>>> current code would not work. Since that is not the case, the change 
>>> would
>>> be purely cosmetic. Also, I still don't see why the -ENODEV check 
>>> would be
>>> necessary.
>>>
>>> Guenter
>>
>> For boards such as S32G274A-EVB, S32G274A-RDB2 and S32G399A-RDB3 which 
>> do not have a voltage regulator, 
>> 'devm_regulator_get_enable_optional()' would return error value -19 
>> (-ENODEV). Also, other usages from the Linux Kernel seem to perform 
>> the same error check when using 'devm_regulator_get_enable_optional()' 
>> [1], [2] and [3].
>>
>> This patch would help in S32G2 and S32G3 to not print an unnecessary 
>> kernel log warning hinting usage of a dummy regulator when such a 
>> regulator is not required according to the binding.
>>
>> Would you like me to send a V2 with the commit title updated as follows ?
>>
>> "
>> hwmon: (ina2xx) make regulator 'vs' support optional
>>
>> According to the 'ti,ina2xx' binding, the 'vs-supply' property is 
>> optional. Furthermore, S32G2/S32G3 based boards which integrate the 
>> ina231 sensor do not have a dedicated voltage regulator. Thus, making 
>> regulator support optional would help in avoiding any unnecessary 
>> kernel log warnings during boot.
>> "
> 
> Make it:
> 
> "According to the 'ti,ina2xx' binding, the 'vs-supply' property is 
> optional.
>   Use devm_regulator_get_enable_optional() to avoid a kernel warning 
> message
>   if the property is not provided.
> "
> 
> Then add a note to the code explaining that the check for -ENODEV is 
> necessary
> because the regulator core returns -ENODEV if the regulator is not 
> available.
> 
> Why it makes sense for this function to return -ENODEV if an _optional_ 
> regulator
> is not available escapes me, but that is a different issue.
> 
> Guenter
> 

Hello Guenter,

Thanks for your review & suggestions.
I will send a V2 patch.


Regards,
Ciprian