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

From: Jonathan Cameron
Date: Wed Jul 05 2017 - 04:07:43 EST


On Wed, 5 Jul 2017 07:37:05 +0000
Nicholas Mc Guire <der.herr@xxxxxxx> 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@xxxxxxxxxxxxxx> wrote:
> >
> > > Hi Nicholas,
> > >
> > > On Sun, May 14, 2017 at 10:43 AM, Nicholas Mc Guire
> > > <der.herr@xxxxxxx> 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@xxxxxxx> ---
> > > >
> > > > 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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