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

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Date:   Tue, 13 Jun 2023 23:26:51 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.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 13/06/2023 18:20:56+0300, Andy Shevchenko wrote:
> On Tue, Jun 13, 2023 at 03:00:07PM +0200, Rasmus Villemoes wrote:
> > Hook up support for reading the values of the SR_LBAT85 and SR_LBAT75
> > bits. Translate the former to "battery low", and the latter to
> > "battery empty or not-present".
> 
> A couple of nit-picks below.
> 
> ...
> 
> > +static int isl12022_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
> > +{
> > +	struct regmap *regmap = dev_get_drvdata(dev);
> > +	u32 user = 0, val;
> 
> This assignment can be done in the actual case below.
> 
> > +	int ret;
> > +
> > +	switch (cmd) {
> > +	case RTC_VL_READ:
> > +		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.
 */

> > +			return ret;
> 
> 		user = 0;
> 
> The rationale to avoid potential mistakes in the future in case this function
> will be expanded and user will be re-used.
> 
> > +		if (val & ISL12022_SR_LBAT85)
> > +			user |= RTC_VL_BACKUP_LOW;
> > +
> > +		if (val & ISL12022_SR_LBAT75)
> > +			user |= RTC_VL_BACKUP_EMPTY;
> > +
> > +		return put_user(user, (u32 __user *)arg);
> > +
> > +	default:
> > +		return -ENOIOCTLCMD;
> > +	}
> > +}
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com