Re: [PATCH 2/4] iio: adc: sd modulator: add scale support

[Olivier MOYSAN]

Hi Jonathan,

On 2/8/20 5:03 PM, Jonathan Cameron wrote:
> On Tue, 4 Feb 2020 11:10:06 +0100
> Olivier Moysan <olivier.moysan@xxxxxx> wrote:
>
>> Add scale support to sigma delta modulator.
>>
>> Signed-off-by: Olivier Moysan <olivier.moysan@xxxxxx>
> I note below that there are probably some complexities around
> whether vref is used as you have it here or not.
>
> A few other bits inline around a race condition introduced in probe / remove.
>
> Thanks,
>
> Jonathan
>
>> ---
>>   drivers/iio/adc/sd_adc_modulator.c | 108 ++++++++++++++++++++++++++---
>>   1 file changed, 100 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/iio/adc/sd_adc_modulator.c b/drivers/iio/adc/sd_adc_modulator.c
>> index 560d8c7d9d86..a83f35832050 100644
>> --- a/drivers/iio/adc/sd_adc_modulator.c
>> +++ b/drivers/iio/adc/sd_adc_modulator.c
>> @@ -10,8 +10,7 @@
>>   #include <linux/iio/triggered_buffer.h>
>>   #include <linux/module.h>
>>   #include <linux/of_device.h>
>> -
>> -static const struct iio_info iio_sd_mod_iio_info;
>> +#include <linux/regulator/consumer.h>
>>   
>>   static const struct iio_chan_spec iio_sd_mod_ch = {
>>   	.type = IIO_VOLTAGE,
>> @@ -21,34 +20,126 @@ static const struct iio_chan_spec iio_sd_mod_ch = {
>>   		.realbits = 1,
>>   		.shift = 0,
>>   	},
>> +	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
> This relies on generic sigma delta modulators using an external vref.
> They might have an internal always on regulator...
> I would suggest we only support scale for devices with explicitly
> defined compatibles where we can know what regulators are used etc.
>
> For many devices, there will be a single powersupply called vdd-supply
> or similar in DT.  It may also provide a reference voltage.
I will remove scale support for generic sd-modulator,
according to your comment on sd modulator bindings.
The DFSDM driver expects scale attribute from sd-modulator.
So, some rework of DFSDM driver will be required
to also support raw data reading.

>> +};
>> +
>> +static const struct iio_chan_spec iio_sd_mod_ch_ads = {
>> +	.type = IIO_VOLTAGE,
>> +	.indexed = 1,
>> +	.scan_type = {
>> +		.sign = 'u',
>> +		.realbits = 1,
>> +		.shift = 0,
>> +	},
>> +	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
>> +	.differential = 1,
>> +};
>> +
>> +struct iio_sd_mod_priv {
>> +	struct regulator *vref;
>> +	int vref_mv;
>> +};
>> +
>> +static int iio_sd_mod_read_raw(struct iio_dev *indio_dev,
>> +			       struct iio_chan_spec const *chan, int *val,
>> +			       int *val2, long mask)
>> +{
>> +	struct iio_sd_mod_priv *priv = iio_priv(indio_dev);
>> +
>> +	switch (mask) {
>> +	case IIO_CHAN_INFO_SCALE:
>> +		*val = priv->vref_mv;
>> +		*val2 = chan->scan_type.realbits;
>> +		return IIO_VAL_INT;
>> +	}
>> +
>> +	return -EINVAL;
>> +}
>> +
>> +static const struct iio_info iio_sd_mod_iio_info = {
>> +	.read_raw = iio_sd_mod_read_raw,
>>   };
>>   
>>   static int iio_sd_mod_probe(struct platform_device *pdev)
>>   {
>>   	struct device *dev = &pdev->dev;
>> +	struct iio_sd_mod_priv *priv;
>>   	struct iio_dev *iio;
>> +	int ret;
>>   
>> -	iio = devm_iio_device_alloc(dev, 0);
>> +	iio = devm_iio_device_alloc(dev, sizeof(*priv));
>>   	if (!iio)
>>   		return -ENOMEM;
>>   
>> +	iio->channels = (const struct iio_chan_spec *)
>> +					of_device_get_match_data(&pdev->dev);
>> +
>> +	priv = iio_priv(iio);
>> +
>>   	iio->dev.parent = dev;
>>   	iio->dev.of_node = dev->of_node;
>>   	iio->name = dev_name(dev);
>>   	iio->info = &iio_sd_mod_iio_info;
>>   	iio->modes = INDIO_BUFFER_HARDWARE;
>> -
>>   	iio->num_channels = 1;
>> -	iio->channels = &iio_sd_mod_ch;
>>   
>>   	platform_set_drvdata(pdev, iio);
>>   
>> -	return devm_iio_device_register(&pdev->dev, iio);
>> +	priv->vref = devm_regulator_get_optional(dev, "vref");
>> +	if (IS_ERR(priv->vref)) {
>> +		ret = PTR_ERR(priv->vref);
>> +		if (ret != -ENODEV) {
>> +			if (ret != -EPROBE_DEFER)
>> +				dev_err(dev, "vref get failed, %d\n", ret);
>> +			return ret;
>> +		}
>> +	}
>> +
>> +	if (!IS_ERR(priv->vref)) {
>> +		ret = regulator_enable(priv->vref);
>> +		if (ret < 0) {
>> +			dev_err(dev, "vref enable failed %d\n", ret);
>> +			return ret;
>> +		}
>> +
>> +		ret = regulator_get_voltage(priv->vref);
>> +		if (ret < 0) {
>> +			dev_err(dev, "vref get failed, %d\n", ret);
>> +			goto err_regulator_disable;
>> +		}
>> +
>> +		priv->vref_mv = ret / 1000;
>> +		dev_dbg(dev, "vref+=%dmV\n", priv->vref_mv);
>> +	}
>> +
>> +	ret = devm_iio_device_register(&pdev->dev, iio);
> This exposes the userspace and in kernel interfaces.  Those
> are partly dependent on the regulator enable you have above.
>
> Using devm_ version fo this interface leaves you with a race in remove.
> The regulator is disabled before you have remove the interfaces that
> will only work if we assume it is still on.
>
> Hence, you should either use devm_add_action_or_reset magic
> to ensure we still do everything in the right order, or do it
> manually by using iio_device_register and iio_device_unregister.
>
I will fix this in v2.

Regards
Olivier
>> +	if (ret < 0) {
>> +		dev_err(dev, "Failed to register sd-modulator, %d\n", ret);
>> +		goto err_regulator_disable;
>> +	}
>> +
>> +	return 0;
>> +
>> +err_regulator_disable:
>> +	regulator_disable(priv->vref);
>> +
>> +	return ret;
>> +}
>> +
>> +static int iio_sd_mod_remove(struct platform_device *pdev)
>> +{
>> +	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
>> +	struct iio_sd_mod_priv *priv = iio_priv(indio_dev);
>> +
>> +	if (priv->vref)
>> +		return regulator_disable(priv->vref);
>> +
>> +	return 0;
>>   }
>>   
>>   static const struct of_device_id sd_adc_of_match[] = {
>> -	{ .compatible = "sd-modulator" },
>> -	{ .compatible = "ads1201" },
>> +	{ .compatible = "sd-modulator", .data = &iio_sd_mod_ch },
>> +	{ .compatible = "ads1201", .data = &iio_sd_mod_ch_ads },
>>   	{ }
>>   };
>>   MODULE_DEVICE_TABLE(of, sd_adc_of_match);
>> @@ -59,6 +150,7 @@ static struct platform_driver iio_sd_mod_adc = {
>>   		.of_match_table = of_match_ptr(sd_adc_of_match),
>>   	},
>>   	.probe = iio_sd_mod_probe,
>> +	.remove = iio_sd_mod_remove,
>>   };
>>   
>>   module_platform_driver(iio_sd_mod_adc);