linux-kernel - Re: [PATCH 1/3] driver core: add probe

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Message-ID: <CAHp75Vd1JQVx96FLEtTO7a7-OBaC1nUKcoSk4S6wvO6BtjJ-3w@mail.gmail.com>
Date:   Wed, 17 Oct 2018 14:33:08 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Mark Brown <broonie@...nel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 1/3] driver core: add probe_err log helper

On Wed, Oct 17, 2018 at 2:29 PM Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
>
> On Tue, Oct 16, 2018 at 04:55:00PM +0300, Andy Shevchenko wrote:
> > On Tue, Oct 16, 2018 at 3:55 PM Andrzej Hajda <a.hajda@...sung.com> wrote:
> > > On 16.10.2018 13:29, Andrzej Hajda wrote:
> > > > On 16.10.2018 13:01, Andy Shevchenko wrote:
> > > >> On Tue, Oct 16, 2018 at 10:22 AM Andrzej Hajda <a.hajda@...sung.com> wrote:
> > > >>> During probe every time driver gets resource it should usually check for error
> > > >>> printk some message if it is not -EPROBE_DEFER and return the error. This
> > > >>> pattern is simple but requires adding few lines after any resource acquisition
> > > >>> code, as a result it is often omited or implemented only partially.
> > > >>> probe_err helps to replace such code seqences with simple call, so code:
> > > >>>         if (err != -EPROBE_DEFER)
> > > >>>                 dev_err(dev, ...);
> > > >>>         return err;
> > > >>> becomes:
> > > >>>         return probe_err(dev, err, ...);
> >
> > > >>> +               va_start(args, fmt);
> > > >>> +
> > > >>> +               vaf.fmt = fmt;
> > > >>> +               vaf.va = &args;
> > > >>> +
> > > >>> +               __dev_printk(KERN_ERR, dev, &vaf);
> >
> > > >> It would be nice to print an error code as well, wouldn't it?
> > > > Hmm, on probe fail error is printed anyway (with exception of
> > > > EPROBE_DEFER, ENODEV and ENXIO):
> > > >     "probe of %s failed with error %d\n"
> > > > On the other side currently some drivers prints the error code anyway
> > > > via dev_err or similar, so I guess during conversion to probe_err it
> > > > should be removed then.
> > > >
> > > > If we add error code to probe_err is it OK to report it this way?
> > > >     dev_err(dev, "%V, %d\n", &vaf, err);
> > >
> > > Ups, I forgot that message passed to probe_err will contain already
> > > newline character.
> >
> > You may consider not to pass it.
>
> It's normal to pass the '\n', so by doing this, we create the situation
> where this function becomes the exception to the norm.  That's not a
> good idea - we will see people forget that appending '\n' should not
> be done for this particular function.
>
> While we could add a checkpatch rule, that's hassle (extra rework).  In
> any case, I think the message would be much better formatted if we did:
>
>         dev_err(dev, "error %d: %V", err, &vaf);
>
> which means we end up with (eg):
>
>         error -5: request_irq failed for irq 9
>
> rather than:
>
>         request_irq failed for irq 9, -5
>
> which is more confusing.

As I said earlier, I'm fine to either variant and I see your point
here, so, I tend to agree to this variant.

P.S. Andrzej, in any case my Rb tag, which I just gave, stays.

-- 
With Best Regards,
Andy Shevchenko