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

Jonathan Cameron
2020-02-08T16:03:34Z

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.

> +};
> +
> +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.

> + 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);