Hi Jonathan,

On 2/8/20 5:03 PM, Jonathan Cameron wrote:

On Tue, 4 Feb 2020 11:10:06 +0100
Olivier Moysan [off-list ref] wrote:

quoted

Add scale support to sigma delta modulator.

Signed-off-by: Olivier Moysan <redacted>

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

quoted

---
  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.

quoted

+};
+
+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

quoted

+	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);