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

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Message-ID: <20170705160647.00001913@huawei.com>
Date:   Wed, 5 Jul 2017 16:06:47 +0800
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Nicholas Mc Guire <der.herr@...r.at>
CC:     Jonathan Cameron <jic23@...nel.org>,
        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 Wed, 5 Jul 2017 07:37:05 +0000
Nicholas Mc Guire <der.herr@...r.at> wrote:

> 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 !
I think Geert's analysis also suggests that you can just drop the last
conditional without changing the code. gcc should be fine with that

Jonathan
> 
> thx!
> hofrat
> --
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