linux-kernel - Re: [PATCH v1 2/4] iio: adc: Add support for MediaTek MT6357/8/9 Auxiliary ADC

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Date: Tue, 4 Jun 2024 13:56:15 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: jic23@...nel.org, lars@...afoo.de, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, matthias.bgg@...il.com, lee@...nel.org,
 andy@...nel.org, nuno.sa@...log.com, bigunclemax@...il.com,
 dlechner@...libre.com, marius.cristea@...rochip.com,
 marcelo.schmitt@...log.com, fr0st61te@...il.com, mitrutzceclan@...il.com,
 mike.looijmans@...ic.nl, marcus.folkesson@...il.com,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH v1 2/4] iio: adc: Add support for MediaTek MT6357/8/9
 Auxiliary ADC

Il 04/06/24 13:05, Andy Shevchenko ha scritto:
> On Tue, Jun 4, 2024 at 1:38 PM AngeloGioacchino Del Regno
> <angelogioacchino.delregno@...labora.com> wrote:
>> Il 30/05/24 15:34, Andy Shevchenko ha scritto:
>>> On Thu, May 30, 2024 at 12:34 PM AngeloGioacchino Del Regno
>>> <angelogioacchino.delregno@...labora.com> wrote:
> 
> ...
> 
>>>> +#define PMIC_RG_RESET_VAL              (BIT(0) | BIT(3))
>>>
>>> In this form it requires a comment explaining each mentioned bit.
>>
>> I don't have an explanation for this, I know it's two different bits from some
>> reveng, but the downstream driver declares that simply as 0x9.
>>
>> Should I just "mask" this as 0x9 instead?
> 
> In this case for all of the questionable forms, please add a oneline
> comment suggesting that "these are different bits without known
> purpose of each." or something like that.
> 

Perfect. Comment added.

> ...
> 
>>>> +#define MT6358_IMP0_CLEAR              (BIT(14) | BIT(7))
>>>
>>> As per above.
>>>
>>
>> Same, I don't have any explanation for that.
>>
>> If you prefer, I can define this as 0x4080, but honestly I prefer keeping
>> it as-is since I am sure it's not a magic number but really two bits to flip
>> in a register.
> 
> As per above.
> 
> ...
> 
>>>> +       u8 r_numerator;
>>>> +       u8 r_denominator;
>>>
>>> Can you add struct u8_fract to the math.h and use it? I will Ack/R the
>>> respective patch.
>>
>> Yeah, I did that exactly because u8_fract wasn't there and I didn't want
>> to waste more bits, but since you just asked for it... well, I'm happier :-)
> 
> Note, it's enough to have my Rb tag and route that change via IIO
> tree. We have done similar way for other changes in math.h (or aline)
> in the past.
> 

Sure.

> ...
> 
>>>> +       /* Assert ADC reset */
>>>> +       regmap_set_bits(regmap, pdata->regs[PMIC_HK_TOP_RST_CON0], PMIC_RG_RESET_VAL);
>>>
>>> No required delay in between?
>>
>> No, as strange as it may look, there is no delay required in between: this is
>> because the register R/W is behind the PMIC Wrapper as much as all of the other
>> MediaTek PMIC (sub)devices, so, missing delays was intentional here, yes.
> 
> Maybe a comment?
> 

Done :-)

/* De-assert ADC reset. No wait required, as pwrap takes care of that for us. */

> ...
> 
>>>> +       mutex_lock(&adc_dev->lock);
>>>
>>> Why not use cleanup.h?
>>
>> I want to unlock the mutex immediately right after executing read_imp() or
>> mt6359_auxadc_read_adc(), and I don't want the reset to be done while a mutex
>> is being held, as that makes no sense for this driver.
> 
> That's why we have scoped_guard(). Exactly for such cases.
> 

Thanks for the hint, looking at other usages that was straightforward.

>> Besides, I find the macros in cleanup.h to be cryptic - in my opinion, they
>> require better documentation as, for example, I don't understand when the
>> guard(mutex)(my_mutex) is supposed to acquire the lock and when it's supposed
>> to release it.
> 
> They are cryptic due to limitations in C language. But for the end
> user it doesn't matter. The behaviour is well understandable and makes
> code cleaner and less prone for errors such as missing unlocks. So,
> please use cleanup.h.
> 

Indeed, but my point was that the documentation can (and probably should)
be improved.


Cheers,
Angelo