linux-kernel - Re: [PATCH v2 2/6] iio: light: Add gain-time-scale helpers

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Message-ID: <ZA81rpWgwvP2bigt@smile.fi.intel.com>
Date:   Mon, 13 Mar 2023 16:39:42 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Matti Vaittinen <mazziesaccount@...il.com>
Cc:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Paul Gazzillo <paul@...zz.com>,
        Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Shreeya Patel <shreeya.patel@...labora.com>,
        Zhigang Shi <Zhigang.Shi@...eon.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] iio: light: Add gain-time-scale helpers

On Mon, Mar 13, 2023 at 01:31:42PM +0200, Matti Vaittinen wrote:
> On 3/6/23 13:13, Andy Shevchenko wrote:
> > On Fri, Mar 03, 2023 at 07:54:22AM +0000, Vaittinen, Matti wrote:
> > > On 3/2/23 17:05, Andy Shevchenko wrote:
> > > > On Thu, Mar 02, 2023 at 12:57:54PM +0200, Matti Vaittinen wrote:

...

> > > > > +		for (i = 0; !ret && i < gts->num_avail_all_scales; i++)
> > > > 
> > > > Much easier to read if you move this...
> > > > 
> > > > > +			ret = iio_gts_total_gain_to_scale(gts, all_gains[i],
> > > > > +					&gts->avail_all_scales_table[i * 2],
> > > > > +					&gts->avail_all_scales_table[i * 2 + 1]);
> > > > 
> > > > ...here as
> > > > 
> > > > 		if (ret)
> > > > 			break;
> > > 
> > > I think the !ret in loop condition is obvious. Adding break and brackets
> > > would not improve this.
> > 
> > It moves it to the regular pattern. Yours is not so distributed in the kernel.
> 
> I believe we can find examples of both patterns in kernel. I don't think the
> "many people use different pattern" is a great reason to add break +
> brackets which (in my eyes) give no additional value to code I am planning
> to keep reading also in the future...

The problem is that your pattern is not so standard (distributed) and hence
less maintainable.

...

> > > > > +			if (!diff) {
> > > > 
> > > > Why not positive conditional?
> > > 
> > > Because !diff is a special condition and we check explicitly for it.
> > 
> > And how my suggestion makes it different?
> 
> In example you gave we would be checking if the value is anything else but
> the specific value we are checking for. It is counter intuitive.
> 
> > (Note, it's easy to miss the ! in the conditionals, that's why positive ones
> >   are preferable.)
> 
> Thank you for explaining me the rationale behind the "positive checks". I
> didn't know missing '!' was seen as a thing.
> 
> I still don't think being afraid of missing '!' is a good reason to switch
> to counter intuitive checks. A check "if (!foo)" is a pattern in-kernel if
> anything and in my opinion people really should be aware of it.
> 
> (I would much more say that having a constant value on left side of a
> "equality" check is beneficial as people do really occasionally miss one '='
> when meaning '=='. Still, this is not strong enough reason to make
> counter-intuitive checks. In my books 'avoiding negative checks' is much
> less of a reason as people (in my experience) do not really miss the '!'.)

It's not a problem when it's a common pattern (like you mentioned
if (!foo) return -ENOMEM; or alike), but in your case it's not.
I would rather see if (diff == 0) which definitely shows the intention
and I wouldn't tell a word against it.

-- 
With Best Regards,
Andy Shevchenko