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

Olivier MOYSAN
2020-02-11T15:22:38Z

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@st.com> wrote:
>
>> Add scale support to sigma delta modulator.
>>
>> Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
> 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);