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Date:   Wed, 9 Sep 2020 09:37:16 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Krzysztof Kozlowski <krzk@kernel.org>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Andrzej Hajda <a.hajda@samsung.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Joe Perches <joe@perches.com>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Subject: Re: [PATCH v1] driver core: Annotate dev_err_probe() with
 __must_check
Message-ID: <20200909073716.GA560912@kroah.com>
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On Wed, Sep 09, 2020 at 09:08:14AM +0200, Krzysztof Kozlowski wrote:
> On Wed, 9 Sep 2020 at 09:02, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > On Wed, Sep 09, 2020 at 08:29:25AM +0200, Krzysztof Kozlowski wrote:
> > > On Wed, 26 Aug 2020 at 18:18, Joe Perches <joe@perches.com> wrote:
> > > >
> > > > On Wed, 2020-08-26 at 18:55 +0300, Andy Shevchenko wrote:
> > > > > On Wed, Aug 26, 2020 at 08:44:30AM -0700, Joe Perches wrote:
> > > > > > On Wed, 2020-08-26 at 13:44 +0300, Andy Shevchenko wrote:
> > > > >
> > > > > ...
> > > > >
> > > > > > > -int dev_err_probe(const struct device *dev, int err, const char *fmt, ...);
> > > > > > > +int __must_check dev_err_probe(const struct device *dev, int err, const char *fmt, ...);
> > >
> > > +Cc Stephen and Greg,
> > >
> > > Hi Andy,
> > >
> > > Did this patch ended up in next somehow? I am surprised because now I
> > > got warnings for perfectly fine code:
> > > https://lore.kernel.org/linux-next/20200909155654.76fe3bd6@canb.auug.org.au/T/#u
> > >
> > > This creates simply false warnings instead of hints for "optimization".
> >
> > Yes, it got merged into m y driver core tree.
> >
> > I'll fix up the tty build warning, should be easy enough, the patch is
> > below.
> 
> Yes, this fix suppresses the warning but the question is whether we
> really want the warning?
> Such fixes mean additional code which the compiler might not optimize
> (unless it inlines the dev_err_probe()). This additional code is
> purely for suppressing the warning, without any meaning on its own.
> Actually it might be even confusing for someone to see:
> if (ret)
>   ret = dev_err_probe(ret);

Yeah, that is dumb, as the patch I made shows :(

> warn_unused_result should point errors, not "optimization
> opportunities". If you want to have opportunity, add a coccinelle
> rule. Or a checkpatch rule. Not a compiler warning.

Ok, I now agree, I'll go revert this patch and trust that driver authors
will "do the right thing" here...

thanks,

greg k-h