On Wed, Sep 22, 2021 at 10:48:45AM -0400, Liam Beguin wrote:
> Hi Dan,
>
> On Wed, Sep 22, 2021 at 09:00:26AM +0300, Dan Carpenter wrote:
> > On Wed, Sep 22, 2021 at 01:10:52AM -0400, Liam Beguin wrote:
> > > >
> > > > 369 if (IS_ERR(ad7949_adc->vref)) {
> > > > 370 ret = PTR_ERR(ad7949_adc->vref);
> > > > 371 if (ret != -ENODEV)
> > > > 372 return ret;
> > > > 373 /* unbuffered? */
> > > > 374 ad7949_adc->vref = devm_regulator_get_optional(dev, "vref");
> > > > 375 if (IS_ERR(ad7949_adc->vref)) {
> > > > 376 ret = PTR_ERR(ad7949_adc->vref);
> > > > 377 if (ret != -ENODEV)
> > > > 378 return ret;
> > > >
> > > > Instead of returning NULL when the regulator is disabled it returns
> > > > -ENODEV. How do you differentiate from an -ENODEV which is caused by an
> > > > error vs an -ENODEV which is caused because the optional regulator is
> > > > disabled? You'll just have to hope that the errors are less common and
> > > > assume it means disabled.
> > >
> > > I see.. So far, I've only used fixed-regulators to provide a constant
> > > voltage reference here, and I guess those are quite unlikely to fail.
> > >
> > > > You might be doubting that devm_regulator_get_optional() can return
> > > > -ENODEV on error? Look at the code and prepare your heart for sadness.
> > >
> > > Thanks for the warning, I see what you meant now.
> > >
> > > I wasn't able to use smatch to reproduce the error with the following:
> > >
> > > make O=builds/smatch CHECK="~/dev/smatch/smatch -p=kernel" C=1 Image.gz
> > >
> > > Would you have any pointer for that?
> >
> > This requires building the cross function Database:
> >
> > ~/dev/smatch/smatch_scripts/build_kernel_data.sh
> >
> > The command takes 5 hours to run so here is a short cut which just
> > builds the minimum two files:
> >
> > ~/dev/smatch/smatch_scripts/kchecker --info drivers/regulator/core.c | tee out
> > ~/dev/smatch/smatch_data/db/create_db.sh -p=kernel out
> > ~/dev/smatch/smatch_scripts/kchecker --info drivers/regulator/devres.c | tee out
> > ~/dev/smatch/smatch_data/db/reload_partial.sh out
> > ~/dev/smatch/smatch_scripts/kchecker --spammy drivers/iio/adc/ad7949.c
>
> Thanks, I appreciate the shortcuts! I was able to reproduce the error
> with these steps.
>
> > > Anyway, I believe the following would address the error you mentioned.
> > >
> > > -- >8 --
> > > diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
> > > index 44bb5fde83de..3613f4e55e1c 100644
> > > --- a/drivers/iio/adc/ad7949.c
> > > +++ b/drivers/iio/adc/ad7949.c
> > > @@ -368,12 +368,14 @@ static int ad7949_spi_probe(struct spi_device *spi)
> > > ad7949_adc->vref = devm_regulator_get_optional(dev, "vrefin");
> > > if (IS_ERR(ad7949_adc->vref)) {
> > > ret = PTR_ERR(ad7949_adc->vref);
> > > + ad7949_adc->vref = NULL;
> >
> > This is not required because it will just be reassigned in a couple
> > lines.
>
> Right, sorry about that.
>
> > > if (ret != -ENODEV)
> > > return ret;
> > > /* unbuffered? */
> > > ad7949_adc->vref = devm_regulator_get_optional(dev, "vref");
> > > if (IS_ERR(ad7949_adc->vref)) {
> > > ret = PTR_ERR(ad7949_adc->vref);
> > > + ad7949_adc->vref = NULL;
> >
> > But this also won't work. Passing a NULL to regulator_enable() will
> > cause an Oops. All the reference to ->vref need checks. :/
>
> I believe it still work since these conditions around
> devm_regulator_get_optional() also set ad7949_adc->refsel.
>
> ad7949_adc->refsel is then checked before calling regulator_enable() and
> regulator_get_voltage().
>
> Even without the patch, I don't think we can call regulor_enable()
> without having it be defined. Am I missing something else?
Actually, you're right. This warning is a 100% false positive. Smatch
doesn't handle bit wise tests very well. I've been meaning to write
that code but I haven't done it yet. When I do the false positive will
go away.
Sorry for the noise on this.
regards,
dan carpenter
