linux-kernel - Re: [PATCH v2 2/2] iio: light: Add support for APDS9306 Light Sensor

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Message-ID: <6d553aaa-279f-48bf-96c9-30fdac1ae372@gmail.com>
Date:   Wed, 1 Nov 2023 08:16:32 +0200
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Subhajit Ghosh <subhajit.ghosh@...aklogic.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Paul Gazzillo <paul@...zz.com>,
        Matt Ranostay <matt@...ostay.sg>,
        Stefan Windfeldt-Prytz <stefan.windfeldt-prytz@...s.com>,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] iio: light: Add support for APDS9306 Light Sensor

On 10/31/23 15:42, Andy Shevchenko wrote:
> On Tue, Oct 31, 2023 at 02:07:46PM +0200, Matti Vaittinen wrote:
>> On 10/31/23 12:38, Andy Shevchenko wrote:
>>> On Tue, Oct 31, 2023 at 09:11:37AM +0200, Matti Vaittinen wrote:
>>>> On 10/30/23 12:21, Matti Vaittinen wrote:
>>>>> On 10/29/23 17:51, Matti Vaittinen wrote:
>>>>>> On 10/28/23 18:20, Jonathan Cameron wrote:
> 
> ...
> 
>>>> 	tmp = gts->max_scale;
>>>>
>>>> 	rem = do_div(tmp, total_gain);
>>>> 	if (total_gain > 1 && rem >= total_gain / 2)
>>>> 		tmp += 1ULL;
>>>
>>> ...which is NIH DIV_ROUND_CLOSEST_ULL()
>>
>> There is a difference though. The DIV_ROUND_CLOSEST_ULL() does
>>
>> tmp + total_gain / 2;
>>
>> before division - which in theory may overflow.
> 
> Then you can fix it there for everybody, no?

Now that I know of this macro - Maybe. It's just always scary to touch 
things which seem like fundamental building blocks and which may be used 
by many. Odds are something breaks, so I tend to be very conservative 
when suggesting changes to widely used stuff. Especially when I have no 
idea when and why the API has been added - and if the thing I'm trying 
to "fix" has been a deliberate choice.

Yours,
	-- Matti.

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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