linux-kernel - Re: [PATCH v2 5/8] rtc: isl12022: implement RTC_VL

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Date:   Wed, 14 Jun 2023 18:13:52 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/8] rtc: isl12022: implement RTC_VL_READ ioctl

On Wed, Jun 14, 2023 at 03:50:36PM +0200, Alexandre Belloni wrote:
> On 14/06/2023 15:16:14+0300, Andy Shevchenko wrote:
> > On Tue, Jun 13, 2023 at 11:26:51PM +0200, Alexandre Belloni wrote:
> > > On 13/06/2023 18:20:56+0300, Andy Shevchenko wrote:
> > > > On Tue, Jun 13, 2023 at 03:00:07PM +0200, Rasmus Villemoes wrote:

...

> > > > > +		ret = regmap_read(regmap, ISL12022_REG_SR, &val);
> > > > > +		if (ret < 0)
> > > > 
> > > > I always feel uneasy with ' < 0' — Does positive error makes sense?
> > > > Is it even possible? OTOH if the entire driver uses this idiom...
> > > > oh well, let's make it consistent.
> > > 
> > > /**
> > >  * regmap_read() - Read a value from a single register
> > >  *
> > >  * @map: Register map to read from
> > >  * @reg: Register to be read from
> > >  * @val: Pointer to store read value
> > >  *
> > >  * A value of zero will be returned on success, a negative errno will
> > >  * be returned in error cases.
> > >  */
> > 
> > I'm not sure what you meant by this. Yes, I know that there is no
> > possibility that regmap API returns positive value. Do you mean that
> > regmap API documentation is unclear?
> 
> No, I mean that you'd have to be clearer as to why you are uneasy with a
> test for a negative value when the function returns 0 for success and a
> negative value for an error. Else, this is pure bullying.

>From the perspective of the code reader, a person, who might have not known all
the implementation details of the calls this kind of check will always puzzle
about positive value.

When reading such a code the following questions are arisen:
1) Can the positive return value be the case?
2) If so, what is the meaning of a such?
3) Why do we not care about it?

All this can simply gone if we use

	ret = foo(...);
	if (ret)
		return ret;

As it's clear that whatever is non-zero we accept as something to be promoted
to the upper layer. I hope this explains my position.

> > > > > +			return ret;

-- 
With Best Regards,
Andy Shevchenko