Re: [RFC v4 3/3] iio: potentiostat: add LMP91000 support

[Jonathan Cameron <jic23@kernel.org>]

On 20/08/16 04:17, Matt Ranostay wrote:
> Add support for the LMP91000 potentiostat which is used for chemical
> sensing applications.
> 
> Signed-off-by: Matt Ranostay <mranostay@gmail.com>
As this is 'unusual' I'd appreciate more docs in general of what is
going on.

Mostly looking good but few bits and bobs that I think need tweaking inline.

I'd be inclined to factor out the relevant code in industrialio-trigger.c
(iio_trigger_write_current) to do validation etc as well on this.
It's not strickly necessary but might be nice. Also you can then put
a 'exclusive' mode check in there to prevent sysfs writes changing the
trigger on you.

> ---
>  .../bindings/iio/potentiostat/lmp91000.txt         |  30 ++
>  drivers/iio/Kconfig                                |   1 +
>  drivers/iio/Makefile                               |   1 +
>  drivers/iio/potentiostat/Kconfig                   |  22 ++
>  drivers/iio/potentiostat/Makefile                  |   6 +
>  drivers/iio/potentiostat/lmp91000.c                | 377 +++++++++++++++++++++
>  6 files changed, 437 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/potentiostat/lmp91000.txt
>  create mode 100644 drivers/iio/potentiostat/Kconfig
>  create mode 100644 drivers/iio/potentiostat/Makefile
>  create mode 100644 drivers/iio/potentiostat/lmp91000.c
> 
> diff --git a/Documentation/devicetree/bindings/iio/potentiostat/lmp91000.txt b/Documentation/devicetree/bindings/iio/potentiostat/lmp91000.txt
> new file mode 100644
> index 000000000000..b9b621e94cd7
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/potentiostat/lmp91000.txt
> @@ -0,0 +1,30 @@
> +* Texas Instruments LMP91000 potentiostat
> +
> +http://www.ti.com/lit/ds/symlink/lmp91000.pdf
> +
> +Required properties:
> +
> +  - compatible: should be "ti,lmp91000"
> +  - reg: the I2C address of the device
> +  - io-channels: the phandle of the iio provider
> +
> +  - ti,external-tia-resistor: if the property ti,tia-gain-ohm is not defined this
> +    needs to be set to signal that an external resistor value is being used.
> +
> +Optional properties:
> +
> +  - ti,tia-gain-ohm: ohm value of the internal resistor for the transimpedance
> +    amplifier. Must be 2750, 3500, 7000, 14000, 35000, 120000, or 350000 ohms.
> +
> +  - ti,rload-ohm: ohm value of the internal resistor load applied to the gas
> +    sensor. Must be 10, 33, 50, or 100 (default) ohms.
> +
> +Example:
> +
> +lmp91000@48 {
> +	compatible = "ti,lmp91000";
> +	reg = <0x48>;
> +	ti,tia-gain-ohm = <7500>;
> +	ti,rload = <100>;
> +	io-channels = <&adc>;
> +};
> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
> index 6743b18194fb..a31a8cf2c330 100644
> --- a/drivers/iio/Kconfig
> +++ b/drivers/iio/Kconfig
> @@ -87,6 +87,7 @@ if IIO_TRIGGER
>     source "drivers/iio/trigger/Kconfig"
>  endif #IIO_TRIGGER
>  source "drivers/iio/potentiometer/Kconfig"
> +source "drivers/iio/potentiostat/Kconfig"
>  source "drivers/iio/pressure/Kconfig"
>  source "drivers/iio/proximity/Kconfig"
>  source "drivers/iio/temperature/Kconfig"
> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
> index 87e4c4369e2f..2b6e2762a886 100644
> --- a/drivers/iio/Makefile
> +++ b/drivers/iio/Makefile
> @@ -29,6 +29,7 @@ obj-y += light/
>  obj-y += magnetometer/
>  obj-y += orientation/
>  obj-y += potentiometer/
> +obj-y += potentiostat/
>  obj-y += pressure/
>  obj-y += proximity/
>  obj-y += temperature/
> diff --git a/drivers/iio/potentiostat/Kconfig b/drivers/iio/potentiostat/Kconfig
> new file mode 100644
> index 000000000000..1e3baf2cc97d
> --- /dev/null
> +++ b/drivers/iio/potentiostat/Kconfig
> @@ -0,0 +1,22 @@
> +#
> +# Potentiostat drivers
> +#
> +# When adding new entries keep the list in alphabetical order
> +
> +menu "Digital potentiostats"
> +
> +config LMP91000
> +	tristate "Texas Instruments LMP91000 potentiostat driver"
> +	depends on I2C
> +	select REGMAP_I2C
> +	select IIO_BUFFER
> +	select IIO_BUFFER_CB
> +	select IIO_TRIGGERED_BUFFER
> +	help
> +	  Say yes here to build support for the Texas Instruments
> +	  LMP91000 digital potentiostat chip.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called lmp91000
> +
> +endmenu
> diff --git a/drivers/iio/potentiostat/Makefile b/drivers/iio/potentiostat/Makefile
> new file mode 100644
> index 000000000000..64d315ef4449
> --- /dev/null
> +++ b/drivers/iio/potentiostat/Makefile
> @@ -0,0 +1,6 @@
> +#
> +# Makefile for industrial I/O potentiostat drivers
> +#
> +
> +# When adding new entries keep the list in alphabetical order
> +obj-$(CONFIG_LMP91000) += lmp91000.o
> diff --git a/drivers/iio/potentiostat/lmp91000.c b/drivers/iio/potentiostat/lmp91000.c
> new file mode 100644
> index 000000000000..5046d2d3da98
> --- /dev/null
> +++ b/drivers/iio/potentiostat/lmp91000.c
> @@ -0,0 +1,377 @@
> +/*
> + * lmp91000.c - Support for Texas Instruments digital potentiostats
> + *
> + * Copyright (C) 2016 Matt Ranostay <mranostay@gmail.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * TODO: bias voltage + polarity control, and multiple chip support
> + */
> +
> +#include <linux/module.h>
> +#include <linux/i2c.h>
> +#include <linux/delay.h>
> +#include <linux/of.h>
> +#include <linux/regmap.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/consumer.h>
> +#include <linux/iio/trigger.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/triggered_buffer.h>
> +
> +#define LMP91000_REG_LOCK		0x01
> +#define LMP91000_REG_TIACN		0x10
> +#define LMP91000_REG_TIACN_GAIN_SHIFT	2
> +
> +#define LMP91000_REG_REFCN		0x11
> +#define LMP91000_REG_REFCN_EXT_REF	0x20
> +#define LMP91000_REG_REFCN_50_ZERO	0x80
> +
> +#define LMP91000_REG_MODECN		0x12
> +#define LMP91000_REG_MODECN_3LEAD	0x03
> +#define LMP91000_REG_MODECN_TEMP	0x07
> +
> +#define LMP91000_DRV_NAME	"lmp91000"
> +
> +static const int lmp91000_tia_gain[] = { 0, 2750, 3500, 7000, 14000, 35000,
> +					 120000, 350000 };
> +
> +static const int lmp91000_rload[] = { 10, 33, 50, 100 };
> +
> +static const struct regmap_config lmp91000_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +};
> +
> +struct lmp91000_data {
> +	struct regmap *regmap;
> +	struct device *dev;
> +
> +	struct iio_trigger *trig;
> +	struct iio_cb_buffer *cb_buffer;
> +
> +	struct completion completion;
> +	u8 chan_select;
> +
> +	u32 buffer[4]; /* 64-bit data + 64-bit timestamp */
> +};
> +
> +static const struct iio_chan_spec lmp91000_channels[] = {
> +	{ /* chemical channel mV */
> +		.type = IIO_VOLTAGE,
> +		.channel = 0,
> +		.indexed = 1,
> +		.address = LMP91000_REG_MODECN_3LEAD,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> +		.scan_index = 0,
> +		.scan_type = {
> +			.sign = 's',
> +			.realbits = 32,
> +			.storagebits = 32,
> +		},
> +	},
> +	IIO_CHAN_SOFT_TIMESTAMP(1),
> +	{ /* temperature channel mV */
> +		.type = IIO_VOLTAGE,
> +		.channel = 1,
> +		.indexed = 1,
> +		.address = LMP91000_REG_MODECN_TEMP,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> +		.scan_index = -1,
> +	},
> +};
> +
> +static int lmp91000_read(struct lmp91000_data *data, int channel, int *val)
> +{
> +	int state, ret;
> +
> +	ret = regmap_read(data->regmap, LMP91000_REG_MODECN, &state);
> +	if (ret)
> +		return -EINVAL;
> +
> +	ret = regmap_write(data->regmap, LMP91000_REG_MODECN, channel);
> +	if (ret)
> +		return -EINVAL;
> +
> +	/* delay till first temperature reading is complete */
> +	if ((state != channel) && (channel == LMP91000_REG_MODECN_TEMP))
> +		usleep_range(3000, 4000);
> +
> +	data->chan_select = channel != LMP91000_REG_MODECN_3LEAD;
> +
I'd like a comment here to explain that this is causing the sample to
be taken.

To get it clear in my head:
1) Calls handle_nested_irq (should rename this function in general as my
understanding of the meaning of chained interrupts was actually wrong when
I came up with this name).
2) poll func of the ADC is called (bottom half only, but that's fine).
3) This calls iio_push_to_buffer.
4) The demux plucks on the relevant channel (only one enabled so that's easy
:) and passes it on to the callback buffer.
5) The completion below finishes, data is copied out and pushed into the
buffer of this device with a timestamp added etc. Job done.

> +	iio_trigger_poll_chained(data->trig);
> +
> +	ret = wait_for_completion_timeout(&data->completion, HZ);
> +	reinit_completion(&data->completion);
> +
> +	if (!ret)
> +		return -ETIMEDOUT;
> +
> +	*val = data->buffer[data->chan_select];
> +
> +	return 0;
> +}
> +
> +static irqreturn_t lmp91000_buffer_handler(int irq, void *private)
> +{
> +	struct iio_poll_func *pf = private;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	struct lmp91000_data *data = iio_priv(indio_dev);
> +	int ret, val;
> +
> +	memset(data->buffer, 0, sizeof(data->buffer));
> +
> +	ret = iio_channel_start_all_cb(data->cb_buffer);
> +	if (ret)
> +		goto error_out;
Why the need for the explicit start each time?  You have control of the
trigger so it shouldn't capture otherwise.  This is a fairly heavy weight
operation so best avoided if we can keep it running across multiple scans.

Would have thought you can just do this in the postenable callback. Then
disable in the predisable.
> +
> +	ret = lmp91000_read(data, LMP91000_REG_MODECN_3LEAD, &val);
> +	iio_channel_stop_all_cb(data->cb_buffer);
> +
> +	if (!ret) {
> +		data->buffer[0] = val;
> +		iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> +						   iio_get_time_ns(indio_dev));
> +	}
> +
> +error_out:
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int lmp91000_read_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan,
> +			     int *val, int *val2, long mask)
> +{
> +	struct lmp91000_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	if (mask != IIO_CHAN_INFO_RAW)
> +		return -EINVAL;
> +
I'd protect this with claim_direct.  We don't want this occuring
mid way through a buffered read - or two of these happening at
once.

> +	ret = iio_channel_start_all_cb(data->cb_buffer);
> +	if (ret)
> +		return ret;
> +
> +	ret = lmp91000_read(data, chan->address, val);
> +
> +	iio_channel_stop_all_cb(data->cb_buffer);
> +
> +	if (!ret)
> +		return IIO_VAL_INT;
> +
> +	return ret;
> +}
> +
> +static const struct iio_info lmp91000_info = {
> +	.driver_module = THIS_MODULE,
> +	.read_raw = lmp91000_read_raw,
> +};
> +
> +static int lmp91000_read_config(struct lmp91000_data *data)
> +{
> +	struct device *dev = data->dev;
> +	struct device_node *np = dev->of_node;
> +	unsigned int reg, val;
> +	int i, ret;
> +
> +	ret = of_property_read_u32(np, "ti,tia-gain-ohm", &val);
> +	if (ret) {
> +		if (of_property_read_bool(np, "ti,external-tia-resistor"))
> +			val = 0;
> +		else {
> +			dev_err(dev, "no ti,tia-gain-ohm defined");
> +			return ret;
> +		}
> +	}
> +
> +	ret = -EINVAL;
> +	for (i = 0; i < ARRAY_SIZE(lmp91000_tia_gain); i++) {
> +		if (lmp91000_tia_gain[i] == val) {
> +			reg = i << LMP91000_REG_TIACN_GAIN_SHIFT;
> +			ret = 0;
> +			break;
> +		}
> +	}
> +
> +	if (ret) {
> +		dev_err(dev, "invalid ti,tia-gain-ohm %d\n", val);
> +		return ret;
> +	}
> +
> +	ret = of_property_read_u32(np, "ti,rload-ohm", &val);
> +	if (ret) {
> +		val = 100;
> +		dev_info(dev, "no ti,rload-ohm defined, default to %d\n", val);
> +	}
> +
> +	ret = -EINVAL;
> +	for (i = 0; i < ARRAY_SIZE(lmp91000_rload); i++) {
> +		if (lmp91000_rload[i] == val) {
> +			reg |= i;
> +			ret = 0;
> +			break;
> +		}
> +	}
> +
> +	if (ret) {
> +		dev_err(dev, "invalid ti,rload-ohm %d\n", val);
> +		return ret;
> +	}
> +
> +	regmap_write(data->regmap, LMP91000_REG_LOCK, 0);
> +	regmap_write(data->regmap, LMP91000_REG_TIACN, reg);
> +	regmap_write(data->regmap, LMP91000_REG_REFCN, LMP91000_REG_REFCN_EXT_REF
> +					| LMP91000_REG_REFCN_50_ZERO);
> +	regmap_write(data->regmap, LMP91000_REG_LOCK, 1);
> +
> +	return 0;
> +}
> +
> +static int lmp91000_buffer_cb(const void *val, void *private)
> +{
> +	struct iio_dev *indio_dev = private;
> +	struct lmp91000_data *data = iio_priv(indio_dev);
> +
> +	data->buffer[data->chan_select] = *((int *)val);
> +	complete_all(&data->completion);
> +
> +	return 0;
> +}
> +
> +static const struct iio_trigger_ops lmp91000_trigger_ops = {
> +	.owner = THIS_MODULE,
> +};
> +
> +static int lmp91000_probe(struct i2c_client *client,
> +			  const struct i2c_device_id *id)
> +{
> +	struct device *dev = &client->dev;
> +	struct lmp91000_data *data;
> +	struct iio_dev *indio_dev;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	indio_dev->info = &lmp91000_info;
> +	indio_dev->channels = lmp91000_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(lmp91000_channels);
> +	indio_dev->name = LMP91000_DRV_NAME;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	i2c_set_clientdata(client, indio_dev);
> +
> +	data = iio_priv(indio_dev);
> +	data->dev = dev;
> +	data->regmap = devm_regmap_init_i2c(client, &lmp91000_regmap_config);
> +	if (IS_ERR(data->regmap)) {
> +		dev_err(dev, "regmap initialization failed.\n");
> +		return PTR_ERR(data->regmap);
> +	}
> +
> +	data->trig = devm_iio_trigger_alloc(data->dev, "%s-mux%d",
> +					    indio_dev->name, indio_dev->id);
> +	if (!data->trig) {
> +		dev_err(dev, "cannot allocate iio trigger.\n");
> +		return -ENOMEM;
> +	}
> +
> +	data->trig->ops = &lmp91000_trigger_ops;
> +	data->trig->dev.parent = dev;
> +	init_completion(&data->completion);
> +
> +	ret = lmp91000_read_config(data);
> +	if (ret)
> +		return ret;
> +
> +	data->cb_buffer = iio_channel_get_all_cb(dev, &lmp91000_buffer_cb,
> +						 indio_dev);
> +	if (IS_ERR(data->cb_buffer)) {
> +		if (PTR_ERR(data->cb_buffer) == -ENODEV)
> +			return -EPROBE_DEFER;
> +		return PTR_ERR(data->cb_buffer);
> +	}
> +
> +	ret = iio_triggered_buffer_setup(indio_dev, NULL,
> +					 &lmp91000_buffer_handler, NULL);
> +	if (ret)
> +		goto error_unreg_cb_buffer;
> +
> +	ret = iio_trigger_register(data->trig);
> +	if (ret) {
> +		dev_err(dev, "cannot register iio trigger.\n");
> +		goto error_unreg_cb_buffer;
> +	}
> +
> +	ret = iio_device_register(indio_dev);
> +	if (ret)
> +		goto error_unreg_buffer;
> +

> +	iio_channel_cb_get_iio_dev(data->cb_buffer)->trig =
> +					iio_trigger_get(data->trig);

Hmm. Is this really all there is to it?

* What prevents the trigger from being changed?  The buffer is only enabled
  currently during each reading so there is plenty of time to 'steal' it.
  We need some for of 'exclusive' lock on this. As we are explicitly clocking
  the ADC capture from here I can't see where a non exclusive mode would work
  without some very very fiddly handling.

* I'd prefer this happening through a utility function as it's more
  that possible it'll be used in drivers that don't know about struct iio_dev.
  So keep that opaque.

It's racey with the iio_device_register... So probably needs to be
prior to that.  I'd even be inclined to work out how to do the cb_buffer
start in the probe and stop in the remove.  I'm not 100% sure all the
infrastructure is in place before the iio_device_register though. If it's
not we may need ot think about adding another stage for this usecase.
Might just push races into iio_device_register itself.

> +
> +	return 0;
> +
> +error_unreg_buffer:
> +	iio_triggered_buffer_cleanup(indio_dev);
> +	iio_trigger_unregister(data->trig);
> +
> +error_unreg_cb_buffer:
> +	iio_channel_release_all_cb(data->cb_buffer);
> +
> +	return ret;
> +}
> +
> +static int lmp91000_remove(struct i2c_client *client)
> +{
> +	struct iio_dev *indio_dev = i2c_get_clientdata(client);
> +	struct lmp91000_data *data = iio_priv(indio_dev);
> +
> +	iio_device_unregister(indio_dev);
> +
> +	iio_channel_stop_all_cb(data->cb_buffer);
> +	iio_channel_release_all_cb(data->cb_buffer);
> +
> +	iio_triggered_buffer_cleanup(indio_dev);
> +	iio_trigger_unregister(data->trig);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id lmp91000_of_match[] = {
> +	{ .compatible = "ti,lmp91000", },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, lmp91000_of_match);
> +
> +static const struct i2c_device_id lmp91000_id[] = {
> +	{ "lmp91000", 0 },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(i2c, lmp91000_id);
> +
> +static struct i2c_driver lmp91000_driver = {
> +	.driver = {
> +		.name = LMP91000_DRV_NAME,
> +		.of_match_table = of_match_ptr(lmp91000_of_match),
> +	},
> +	.probe = lmp91000_probe,
> +	.remove = lmp91000_remove,
> +	.id_table = lmp91000_id,
> +};
> +module_i2c_driver(lmp91000_driver);
> +
> +MODULE_AUTHOR("Matt Ranostay <mranostay@gmail.com>");
> +MODULE_DESCRIPTION("LMP91000 digital potentiostat");
> +MODULE_LICENSE("GPL");
>