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

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Date:   Wed, 5 Jul 2017 07:37:05 +0000
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        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, Jul 04, 2017 at 08:08:53PM +0100, Jonathan Cameron wrote:
> 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?
> 
Thanks Geert for finding that - yes ret needs to be 
initialized to 0 here, success case as documented in 
the header of zpa2326_wait_oneshot_completion - 
interestingly enough gcc gcc (Debian 4.9.2-10) 4.9.2 
does not flag this uninitioalized variable !

thx!
hofrat