Re: [bug report] iio: adc: ad7949: add vref selection support

[Dan Carpenter <dan.carpenter@oracle.com>]

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

> 
> 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.

>  		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.  :/

>  			if (ret != -ENODEV)
>  				return ret;
>  		} else {

regards,
dan carpenter