Re: [PATCH v3 2/3] iio: adc: tsc2046: add vref support

[Jonathan Cameron]

On Thu, 1 Sep 2022 06:11:45 +0200
Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> wrote:

> If VREF pin is attached, we should use external VREF source instead of
> the internal. Otherwise we will get wrong measurements on some of channel
> types.
> 
> Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
Hi Oleksij,

I'm not sure why I didn't review this patch in v1...

Anyhow, some comments below.

Jonathan

> ---
>  drivers/iio/adc/ti-tsc2046.c | 64 +++++++++++++++++++++++++++++++-----
>  1 file changed, 55 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti-tsc2046.c b/drivers/iio/adc/ti-tsc2046.c
> index 0d9436a69cbfb..bbc8b4137b0b1 100644
> --- a/drivers/iio/adc/ti-tsc2046.c
> +++ b/drivers/iio/adc/ti-tsc2046.c
> @@ -8,6 +8,7 @@
>  #include <linux/bitfield.h>
>  #include <linux/delay.h>
>  #include <linux/module.h>
> +#include <linux/regulator/consumer.h>
>  #include <linux/spi/spi.h>
>  
>  #include <asm/unaligned.h>
> @@ -175,6 +176,9 @@ struct tsc2046_adc_priv {
>  	u32 time_per_bit_ns;
>  
>  	struct tsc2046_adc_ch_cfg ch_cfg[TI_TSC2046_MAX_CHAN];
> +	bool use_internal_vref;
> +	unsigned int vref_mv;
> +	struct regulator *vref_reg;
>  };
>  
>  #define TI_TSC2046_V_CHAN(index, bits, name)			\
> @@ -252,7 +256,9 @@ static u8 tsc2046_adc_get_cmd(struct tsc2046_adc_priv *priv, int ch_idx,
>  	case TI_TSC2046_ADDR_AUX:
>  	case TI_TSC2046_ADDR_VBAT:
>  	case TI_TSC2046_ADDR_TEMP0:
> -		pd |= TI_TSC2046_SER | TI_TSC2046_PD1_VREF_ON;
> +		pd |= TI_TSC2046_SER;
> +		if (priv->use_internal_vref)
> +			pd |= TI_TSC2046_PD1_VREF_ON;
>  	}
>  
>  	return TI_TSC2046_START | FIELD_PREP(TI_TSC2046_ADDR, ch_idx) | pd;
> @@ -468,7 +474,7 @@ static int tsc2046_adc_read_raw(struct iio_dev *indio_dev,
>  		 * So, it is better to use external voltage-divider driver
>  		 * instead, which is calculating complete chain.
>  		 */
> -		*val = TI_TSC2046_INT_VREF;
> +		*val = priv->vref_mv;
>  		*val2 = chan->scan_type.realbits;
>  		return IIO_VAL_FRACTIONAL_LOG2;
>  	}
> @@ -781,22 +787,42 @@ static int tsc2046_adc_probe(struct spi_device *spi)
>  	indio_dev->num_channels = dcfg->num_channels;
>  	indio_dev->info = &tsc2046_adc_info;
>  
> +	priv->vref_reg = devm_regulator_get_optional(&spi->dev, "vref");
> +	if (!IS_ERR(priv->vref_reg)) {
> +		ret = regulator_enable(priv->vref_reg);
> +		if (ret)
> +			return ret;
> +
> +		ret = regulator_get_voltage(priv->vref_reg);
> +		if (ret < 0)
> +			goto err_regulator_disable;

Whilst regulators voltages of references rarely change at runtime
they are allowed to, so it is logically better to query the
voltage at the point of use. Requests for scale should be
rare (unless there is a consumer that keeps querying this?)
so the slightly overhead there
shouldn't matter.

> +
> +		priv->vref_mv = ret / 1000;
> +		priv->use_internal_vref = false;
> +	} else {
> +		/* Use internal reference */
> +		priv->vref_mv = TI_TSC2046_INT_VREF;
> +		priv->use_internal_vref = true;
> +	}
> +
>  	tsc2046_adc_parse_fwnode(priv);
>  
>  	ret = tsc2046_adc_setup_spi_msg(priv);
>  	if (ret)
> -		return ret;
> +		goto err_regulator_disable;
>  
>  	mutex_init(&priv->slock);
>  
>  	ret = devm_request_irq(dev, spi->irq, &tsc2046_adc_irq,
>  			       IRQF_NO_AUTOEN, indio_dev->name, indio_dev);
>  	if (ret)
> -		return ret;
> +		goto err_regulator_disable;
>  
>  	trig = devm_iio_trigger_alloc(dev, "touchscreen-%s", indio_dev->name);
> -	if (!trig)
> -		return -ENOMEM;
> +	if (!trig) {
> +		ret = -ENOMEM;
> +		goto err_regulator_disable;
> +	}
>  
>  	priv->trig = trig;
>  	iio_trigger_set_drvdata(trig, indio_dev);
> @@ -811,20 +837,39 @@ static int tsc2046_adc_probe(struct spi_device *spi)
>  	ret = devm_iio_trigger_register(dev, trig);
>  	if (ret) {
>  		dev_err(dev, "failed to register trigger\n");
> -		return ret;
> +		goto err_regulator_disable;

Please don't mix devm and non devm calls. It makes it much harder to reason about
the correctness of ordering.
Use devm_add_action_or_reset() to register a callback to disable the
vref regulator.

Alternative is back out the devm_ based registration of everything after
the regulator enable.
>  	}
>  
>  	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
>  					      &tsc2046_adc_trigger_handler, NULL);
>  	if (ret) {
>  		dev_err(dev, "Failed to setup triggered buffer\n");
> -		return ret;
> +		goto err_regulator_disable;
>  	}
>  
>  	/* set default trigger */
>  	indio_dev->trig = iio_trigger_get(priv->trig);
>  
> -	return devm_iio_device_register(dev, indio_dev);
> +	ret = devm_iio_device_register(dev, indio_dev);
> +	if (ret)
> +		goto err_regulator_disable;
> +
> +	return 0;
> +
> +err_regulator_disable:
> +	if (!IS_ERR(priv->vref_reg))
> +		regulator_disable(priv->vref_reg);
> +
> +	return ret;
> +}
> +
> +static void tsc2046_adc_remove(struct spi_device *spi)
> +{
> +	struct iio_dev *indio_dev = spi_get_drvdata(spi);
> +	struct tsc2046_adc_priv *priv = iio_priv(indio_dev);
> +
> +	if (!IS_ERR(priv->vref_reg))
> +		regulator_disable(priv->vref_reg);

>  }
>  
>  static const struct of_device_id ads7950_of_table[] = {
> @@ -839,6 +884,7 @@ static struct spi_driver tsc2046_adc_driver = {
>  		.of_match_table = ads7950_of_table,
>  	},
>  	.probe = tsc2046_adc_probe,
> +	.remove = tsc2046_adc_remove,
>  };
>  module_spi_driver(tsc2046_adc_driver);
>