linux-kernel - Re: [PATCH RFC] iio: pressure: zpa2326: report interrupted case as failure

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Date:   Tue, 4 Jul 2017 20:08:53 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Nicholas Mc Guire <der.herr@...r.at>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        simran singhal <singhalsimran0@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Gregor Boirie <gregor.boirie@...rot.com>,
        linux-iio@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] iio: pressure: zpa2326: report interrupted case as
 failure

On Tue, 4 Jul 2017 12:40:33 +0200
Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> Hi Nicholas,
> 
> On Sun, May 14, 2017 at 10:43 AM, Nicholas Mc Guire <der.herr@...r.at> wrote:
> > If the timeout-case prints a warning message then probably the interrupted
> > case should also. Further, wait_for_completion_interruptible_timeout()
> > returns long not int.
> >
> > Fixes: commit 03b262f2bbf4 ("iio:pressure: initial zpa2326 barometer support")
> > Signed-off-by: Nicholas Mc Guire <der.herr@...r.at>
> > ---
> >
> > The original control-flow was technically not wrong just confusing and a bit
> > complicated. Not clear if reporting the interrupted case actually is useful,
> > but given that the timeout is relatively long (200ms) it is not that unlikely
> > so differentiating the cases seems helpful.
> >
> > Patch was compile-tested with: x86_64_defconfig + CONFIG_IIO=m, CONFIG_ZPA2326=m
> >
> > Patch is against v4.11 (localversion-next is next-20170512)
> >
> >  drivers/iio/pressure/zpa2326.c | 17 ++++++++++-------
> >  1 file changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/iio/pressure/zpa2326.c b/drivers/iio/pressure/zpa2326.c
> > index e58a0ad..617926f 100644
> > --- a/drivers/iio/pressure/zpa2326.c
> > +++ b/drivers/iio/pressure/zpa2326.c
> > @@ -867,12 +867,13 @@ static int zpa2326_wait_oneshot_completion(const struct iio_dev   *indio_dev,
> >  {
> >         int          ret;
> >         unsigned int val;
> > +       long     timeout;
> >
> >         zpa2326_dbg(indio_dev, "waiting for one shot completion interrupt");
> >
> > -       ret = wait_for_completion_interruptible_timeout(
> > +       timeout = wait_for_completion_interruptible_timeout(
> >                 &private->data_ready, ZPA2326_CONVERSION_JIFFIES);
> > -       if (ret > 0)
> > +       if (timeout > 0)  
> 
> Check for strict positive timeout.
> 
> >                 /*
> >                  * Interrupt handler completed before timeout: return operation
> >                  * status.
> > @@ -882,13 +883,15 @@ static int zpa2326_wait_oneshot_completion(const struct iio_dev   *indio_dev,
> >         /* Clear all interrupts just to be sure. */
> >         regmap_read(private->regmap, ZPA2326_INT_SOURCE_REG, &val);
> >
> > -       if (!ret)
> > +       if (!timeout) {  
> 
> Check for zero timeout.
> 
> >                 /* Timed out. */
> > +               zpa2326_warn(indio_dev, "no one shot interrupt occurred (%ld)",
> > +                            timeout);
> >                 ret = -ETIME;
> > -
> > -       if (ret != -ERESTARTSYS)
> > -               zpa2326_warn(indio_dev, "no one shot interrupt occurred (%d)",
> > -                            ret);
> > +       } else if (timeout < 0) {  
> 
> So if we get here, timeout is always strict negative, so the check can
> be removed.
> 
> > +               zpa2326_warn(indio_dev, "wait for one shot interrupt canceled");
> > +               ret = -ERESTARTSYS;
> > +       }
> >
> >         return ret;  
> 
> But gcc-4.1.2 is not smart enough:
> 
> drivers/iio/pressure/zpa2326.c:868: warning: ‘ret’ may be used
> uninitialized in this function
Good analysis.  Care to send the obvious patch?

J
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
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