Re: [PATCH v5 3/5] iio: adc: ad7949: add support for internal vref

["Liam Beguin" <liambeguin@gmail.com>]

On Mon Aug 9, 2021 at 3:42 PM EDT, Jonathan Cameron wrote:
> ...
> > +
> > > >  static int ad7949_spi_probe(struct spi_device *spi)
> > > >  {
> > > >  	u32 spi_ctrl_mask = spi->controller->bits_per_word_mask;
> > > >  	struct device *dev = &spi->dev;
> > > >  	const struct ad7949_adc_spec *spec;
> > > >  	struct ad7949_adc_chip *ad7949_adc;
> > > > +	struct ad7949_channel *ad7949_chan;
> > > > +	struct fwnode_handle *child;
> > > >  	struct iio_dev *indio_dev;
> > > > +	int mode;
> > > > +	u32 tmp;
> > > >  	int ret;
> > > > +	int i;
> > > >  
> > > >  	indio_dev = devm_iio_device_alloc(dev, sizeof(*ad7949_adc));
> > > >  	if (!indio_dev) {
> > > > @@ -343,16 +383,82 @@ static int ad7949_spi_probe(struct spi_device *spi)
> > > >  		return -EINVAL;
> > > >  	}
> > > >  
> > > > -	ad7949_adc->vref = devm_regulator_get(dev, "vref");
> > > > +	/* Setup external voltage ref, buffered? */
> > > > +	ad7949_adc->vref = devm_regulator_get_optional(dev, "vrefin");
> > > >  	if (IS_ERR(ad7949_adc->vref)) {
> > > > -		dev_err(dev, "fail to request regulator\n");
> > > > -		return PTR_ERR(ad7949_adc->vref);
> > > > +		ret = PTR_ERR(ad7949_adc->vref);
> > > > +		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);
> > > > +			if (ret != -ENODEV)
> > > > +				return ret;
> > > > +			/* Internal then */
> > > > +			mode = AD7949_CFG_VAL_REF_INT_4096;
> > > > +		} else {
> > > > +			mode = AD7949_CFG_VAL_REF_EXT_TEMP;
> > > > +		}
> > > > +	} else {
> > > > +		mode = AD7949_CFG_VAL_REF_EXT_TEMP_BUF;
> > > >  	}
> > > >  
> > > > -	ret = regulator_enable(ad7949_adc->vref);
> > > > -	if (ret < 0) {
> > > > -		dev_err(dev, "fail to enable regulator\n");
> > > > -		return ret;
> > > > +	if (mode & AD7949_CFG_VAL_REF_EXTERNAL) {
> > > > +		ret = regulator_enable(ad7949_adc->vref);
> > > > +		if (ret < 0) {
> > > > +			dev_err(dev, "fail to enable regulator\n");
> > > > +			return ret;
> > > > +		}
> > > > +
> > > > +		ret = devm_add_action_or_reset(dev, ad7949_disable_reg,
> > > > +					       ad7949_adc->vref);
> > > > +		if (ret)
> > > > +			return ret;
> > > > +	}
> > > > +
> > > > +	ad7949_adc->channels = devm_kcalloc(dev, spec->num_channels,
> > > > +					    sizeof(*ad7949_adc->channels),
> > > > +					    GFP_KERNEL);
> > > > +	if (!ad7949_adc->channels) {
> > > > +		dev_err(dev, "unable to allocate ADC channels\n");
> > > > +		return -ENOMEM;
> > > > +	}
> > > > +
> > > > +	/* Initialize all channel structures */
> > > > +	for (i = 0; i < spec->num_channels; i++)
> > > > +		ad7949_adc->channels[i].refsel = mode;
> > > > +
> > > > +	/* Read channel specific information form the devicetree */
> > > > +	device_for_each_child_node(dev, child) {
> > > > +		ret = fwnode_property_read_u32(child, "reg", &i);
> > > > +		if (ret) {
> > > > +			dev_err(dev, "missing reg property in %pfw\n", child);
> > > > +			fwnode_handle_put(child);
> > > > +			return ret;
> > > > +		}
> > > > +
> > > > +		ad7949_chan = &ad7949_adc->channels[i];
> > > > +
> > > > +		ret = fwnode_property_read_u32(child, "adi,internal-ref-microvolt", &tmp);
> > > > +		if (ret < 0 && ret != -EINVAL) {
> > > > +			dev_err(dev, "invalid internal reference in %pfw\n", child);
> > > > +			fwnode_handle_put(child);
> > > > +			return ret;
> > > > +		}  
> > 
> > Hi Jonathan,
> > 
> > >
> > > So if we are using external voltage, then we'd not expect this to exist.
> > > ret != -EINVAL should deal with that. However, we then hit the following
> > > switch
> > > and temp isn't set to an appropriate value so we get the error.
> > >
> > > Am I missing something?  
> > 
> > You're right that using an external reference, will cause this to fail.
> > My apologies, I've done a poor job of testing the last two revisions of
> > this patch. I'll do better.
> > 
> > Since a regulator is also required when we're using an external source,
> > I'll add a check for that. Something like this:
> > 
> > 	ret = fwnode_property_read_u32(child, "adi,internal-ref-microvolt", &tmp);
> > 	if (ret == -EINVAL && mode & AD7949_CFG_VAL_REF_EXTERNAL) {
> > 		continue;
> > 	} else if (ret < 0) {
> > 		dev_err(dev, "invalid voltage reference in %pfw\n", child);
> > 		fwnode_handle_put(child);
> > 		return ret;
> > 	}
>
> Makes sense.

Hi Jonathan,

After getting access to another setup to run more tests, I noticed
that setting the reference per channel isn't really feasible.

It take a little while for the reference to be updated internally even
though the request is sent out properly, and reading channels in a
sequence returns bad values.

I'll resend this without the per-channel configuration and make
adi,internal-ref-microvolt a global parameter.

Sorry about that,
Liam

>
> > 
> > Given that we can now have a different scale for each channel based on
> > the vref source, should BIT(IIO_CHAN_INFO_SCALE) be moved to
> > .info_mask_separate in the channel definition?
> Yes, good point.
>
> Hopefully no one will notice the ABI change *crosses fingers*.
>
> Jonathan
>
> > 
> > Thanks,
> > Liam
> > 
> > >  
> > > > +
> > > > +		switch (tmp) {
> > > > +		case 2500000:
> > > > +			ad7949_chan->refsel = AD7949_CFG_VAL_REF_INT_2500;
> > > > +			break;
> > > > +		case 4096000:
> > > > +			ad7949_chan->refsel = AD7949_CFG_VAL_REF_INT_4096;
> > > > +			break;
> > > > +		default:
> > > > +			dev_err(dev, "unsupported internal voltage reference\n");
> > > > +			fwnode_handle_put(child);
> > > > +			return -EINVAL;
> > > > +		}
> > > >  	}
> > > >  
> > > >  	mutex_init(&ad7949_adc->lock);
> > > > @@ -373,7 +479,6 @@ static int ad7949_spi_probe(struct spi_device *spi)
> > > >  
> > > >  err:
> > > >  	mutex_destroy(&ad7949_adc->lock);
> > > > -	regulator_disable(ad7949_adc->vref);
> > > >  
> > > >  	return ret;
> > > >  }
> > > > @@ -385,7 +490,6 @@ static int ad7949_spi_remove(struct spi_device *spi)
> > > >  
> > > >  	iio_device_unregister(indio_dev);
> > > >  	mutex_destroy(&ad7949_adc->lock);
> > > > -	regulator_disable(ad7949_adc->vref);
> > > >  
> > > >  	return 0;
> > > >  }  
> >