linux-kernel - Re: [PATCH v3 08/18] iio: adc: stm32: Simplify with dev_err_probe()

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Date:   Thu, 10 Sep 2020 09:12:08 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
CC:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Tomasz Duszynski <tomasz.duszynski@...akon.com>,
        "Michael Hennerich" <Michael.Hennerich@...log.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        Marek Vasut <marek.vasut@...il.com>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        "linux-amlogic@...ts.infradead.org" 
        <linux-amlogic@...ts.infradead.org>, Peter Rosin <peda@...ntia.se>,
        Jonathan Cameron <jic23@...nel.org>
Subject: Re: [PATCH v3 08/18] iio: adc: stm32: Simplify with dev_err_probe()

On Thu, 10 Sep 2020 08:58:57 +0200
Krzysztof Kozlowski <krzk@...nel.org> wrote:

> On Thu, 10 Sep 2020 at 08:52, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> >
> >
> >
> > On Thursday, September 10, 2020, Peter Rosin <peda@...ntia.se> wrote:  
> >>
> >> Hi!
> >>
> >> On 2020-09-09 21:57, Krzysztof Kozlowski wrote:  
> >> > On Wed, 9 Sep 2020 at 20:36, Jonathan Cameron <jic23@...nel.org> wrote:  
> >> >>
> >> >> On Sat, 29 Aug 2020 08:47:16 +0200
> >> >> Krzysztof Kozlowski <krzk@...nel.org> wrote:
> >> >>  
> >> >>> Common pattern of handling deferred probe can be simplified with
> >> >>> dev_err_probe().  Less code and also it prints the error value.
> >> >>>
> >> >>> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> >> >>> Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
> >> >>>  
> >> >> I don't have the thread to hand, but this tripped a warning next
> >> >> and the patch was dropped as a result. See below.  

oops. That is what I get for reading an email very quickly then looking
at the code a few hours later.  Still a problem here we need to fix
unless I'm missing something.

> >> >
> >> > Thanks for letting me know. If you mean the warning caused by:
> >> > https://lore.kernel.org/lkml/20200909073716.GA560912@kroah.com/
> >> > then the driver-core patch was dropped, not the iio one:
> >> > https://lore.kernel.org/linux-next/20200909074130.GB561485@kroah.com/T/#t
> >> >
> >> > So we are good here :)  
> >>
> >> No, we are definitely not good. See below. That means "See below", and
> >> not "Please take a guess at what is being talking about".  
> >
> >
> >  
> >>  
> >> >>> @@ -596,12 +594,9 @@ static int stm32_adc_core_switches_probe(struct device *dev,
> >> >>>               priv->booster = devm_regulator_get_optional(dev, "booster");
> >> >>>               if (IS_ERR(priv->booster)) {
> >> >>>                       ret = PTR_ERR(priv->booster);
> >> >>> -                     if (ret != -ENODEV) {
> >> >>> -                             if (ret != -EPROBE_DEFER)
> >> >>> -                                     dev_err(dev, "can't get booster %d\n",
> >> >>> -                                             ret);
> >> >>> -                             return ret;
> >> >>> -                     }
> >> >>> +                     if (ret != -ENODEV)
> >> >>> +                             dev_err_probe(dev, ret, "can't get booster\n");  
> >> >>
> >> >> This tripped a warning and got the patch dropped because we no longer
> >> >> return on error.  
> >>
> >> As Jonathan already said, we no longer return in this hunk. I.e., you have
> >> clobbered the error path.  
> >
> >
> > Exactly my point why I proposed _must_check in the first place.  
> 
> That was not exactly that point as you did not mention possible errors
> but only "miss the opportunity to optimize". Optimization is different
> things than a mistake.

In this particular case we have introduced a bug. If the regulator returns
an error other than -ENODEV we will carry on when really should error out.
This includes deferred probe route in which it won't print a message but also won't
actually defer.

Jonathan

> 
> Best regards,
> Krzysztof
> 
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