[PATCH v2] iio: adc: ltc2485: add support for Linear Technology LTC2485 ADC

[PATCH v2] iio: adc: ltc2485: add support for Linear Technology LTC2485 ADC

[Alison Schofield]

Adds basic support for the LTC2485 ADC - a delta-sigma analog-to-digital
converter with an I2C interface that operates in single shot conversion
mode.

The driver supports an on board 5V reference and the power-on default
configuration which rejects both 50hz & 60hz line frequencies and
operates in 1x speed mode.

Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>
---
Changes in v2:
  - changed the wait conversion time function to use monotonic rather than
    real time and to use milliseconds rather than nanoseconds.  
  - made conv time a constant int.

Same notes as in v1:
Reviewers: In addition to commenting on what is present, please comment
on what is absent and the priority in which you would like to see
additional features added to this driver, or needed in this first submittal.

Not supported: 
1. External Vref
2. Additional Configuration Modes
        Temperature Sensor Mode: report temp data (not voltage).

        Line Frequency Rejection Mode: select to reject 50Hz or 60Hz
	or both. (both is default)

        Speed Mode: Default speed mode (1x) performs two conversions each
	cycle and combines the results.  2x speed mode only does one
	conversion each cycle.
3. Power management
4. DT Bindings
5. Triggered buffers
6. What else?


 drivers/iio/adc/Kconfig   |   9 +++
 drivers/iio/adc/Makefile  |   1 +
 drivers/iio/adc/ltc2485.c | 146 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 156 insertions(+)
 create mode 100644 drivers/iio/adc/ltc2485.c

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 1de31bd..a042611 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -264,6 +264,15 @@ config LPC18XX_ADC
 	  To compile this driver as a module, choose M here: the module will be
 	  called lpc18xx_adc.
 
+config LTC2485
+	tristate "Linear Technology LTC2485 ADC driver"
+	depends on I2C
+	help
+	  Say yes here to build support for Linear Technology LTC2485 ADC.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called ltc2485.
+
 config MAX1027
 	tristate "Maxim max1027 ADC driver"
 	depends on SPI
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index 0ba0d50..1be5747 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -27,6 +27,7 @@ obj-$(CONFIG_IMX7D_ADC) += imx7d_adc.o
 obj-$(CONFIG_INA2XX_ADC) += ina2xx-adc.o
 obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
 obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
+obj-$(CONFIG_LTC2485) += ltc2485.o
 obj-$(CONFIG_MAX1027) += max1027.o
 obj-$(CONFIG_MAX1363) += max1363.o
 obj-$(CONFIG_MCP320X) += mcp320x.o
diff --git a/drivers/iio/adc/ltc2485.c b/drivers/iio/adc/ltc2485.c
new file mode 100644
index 0000000..d8f9dac
--- /dev/null
+++ b/drivers/iio/adc/ltc2485.c
@@ -0,0 +1,146 @@
+/*
+ * ltc2485.c - Driver for Linear Technology LTC2485 ADC
+ *
+ * Copyright (C) 2016 Alison Schofield <amsfield22@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Datasheet: http://cds.linear.com/docs/en/datasheet/2485fd.pdf
+ */
+
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+
+/* Power-on configuration: rejects both 50/60Hz, operates at 1x speed */
+#define LTC2485_CONFIG_DEFAULT		0
+
+struct ltc2485_data {
+	struct i2c_client	*client;
+	ktime_t			time_prev;	/* last conversion */
+};
+
+static void ltc2485_wait_conv(struct ltc2485_data *data)
+{
+	const unsigned int conv_time = 147;	/* conversion time ms */
+	unsigned int time_elapsed;
+
+	/* delay if conversion time not passed since last read or write */
+	time_elapsed = ktime_ms_delta(ktime_get(), data->time_prev);
+
+	if (time_elapsed < conv_time)
+		msleep(conv_time - time_elapsed);
+}
+
+static int ltc2485_read(struct ltc2485_data *data, int *val)
+{
+	struct i2c_client *client = data->client;
+	__be32 buf = 0;
+	int ret;
+
+	ltc2485_wait_conv(data);
+
+	ret = i2c_master_recv(client, (char *)&buf, 4);
+	if (ret < 0)  {
+		dev_err(&client->dev, "i2c_master_recv failed\n");
+		return ret;
+	}
+	data->time_prev = ktime_get();
+	*val = sign_extend32(be32_to_cpu(buf) >> 6, 24);
+	return ret;
+}
+
+static int ltc2485_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int *val, int *val2, long mask)
+{
+	struct ltc2485_data *data = iio_priv(indio_dev);
+	int ret;
+
+	if (mask == IIO_CHAN_INFO_RAW) {
+		ret = ltc2485_read(data, val);
+		if (ret < 0)
+			return ret;
+
+		return IIO_VAL_INT;
+
+	} else if (mask == IIO_CHAN_INFO_SCALE) {
+		*val = 5000;			/* on board vref millivolts */
+		*val2 = 25;			/* 25 (24 + sign) data bits */
+		return IIO_VAL_FRACTIONAL_LOG2;
+
+	} else {
+		return -EINVAL;
+	}
+}
+
+static const struct iio_chan_spec ltc2485_channel[] = {
+	{
+		.type = IIO_VOLTAGE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE)
+	},
+};
+
+static const struct iio_info ltc2485_info = {
+	.read_raw = ltc2485_read_raw,
+	.driver_module = THIS_MODULE,
+};
+
+static int ltc2485_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct iio_dev *indio_dev;
+	struct ltc2485_data *data;
+	int ret;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C |
+				     I2C_FUNC_SMBUS_WRITE_BYTE))
+		return -EOPNOTSUPP;
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	i2c_set_clientdata(client, indio_dev);
+	data->client = client;
+
+	indio_dev->dev.parent = &client->dev;
+	indio_dev->name = id->name;
+	indio_dev->info = &ltc2485_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = ltc2485_channel;
+	indio_dev->num_channels = ARRAY_SIZE(ltc2485_channel);
+
+	ret = i2c_smbus_write_byte(data->client, LTC2485_CONFIG_DEFAULT);
+	if (ret < 0)
+		return ret;
+
+	data->time_prev = ktime_get();
+	return devm_iio_device_register(&client->dev, indio_dev);
+}
+
+static const struct i2c_device_id ltc2485_id[] = {
+	{ "ltc2485", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ltc2485_id);
+
+static struct i2c_driver ltc2485_driver = {
+	.driver = {
+		.name = "ltc2485",
+	},
+	.probe = ltc2485_probe,
+	.id_table = ltc2485_id,
+};
+module_i2c_driver(ltc2485_driver);
+
+MODULE_AUTHOR("Alison Schofield <amsfield22@gmail.com>");
+MODULE_DESCRIPTION("Linear Technology LTC2485 ADC driver");
+MODULE_LICENSE("GPL v2");
-- 
2.1.4

Re: [PATCH v2] iio: adc: ltc2485: add support for Linear Technology LTC2485 ADC

[Jonathan Cameron]

On 25/08/16 06:48, Alison Schofield wrote:
> Adds basic support for the LTC2485 ADC - a delta-sigma analog-to-digital
> converter with an I2C interface that operates in single shot conversion
> mode.
> 
> The driver supports an on board 5V reference and the power-on default
> configuration which rejects both 50hz & 60hz line frequencies and
> operates in 1x speed mode.
> 
> Signed-off-by: Alison Schofield <amsfield22@gmail.com>
> Cc: Daniel Baluta <daniel.baluta@gmail.com>
> ---
> Changes in v2:
>   - changed the wait conversion time function to use monotonic rather than
>     real time and to use milliseconds rather than nanoseconds.  
>   - made conv time a constant int.
> 
> Same notes as in v1:
> Reviewers: In addition to commenting on what is present, please comment
> on what is absent and the priority in which you would like to see
> additional features added to this driver, or needed in this first submittal.
None of the below are needed for initially submital.
All 'value' add features at the end of the day. Job one: get reading from
ADC done :)

I made a few really small white space changes and applied this to the
togreg branch of iio.git.  Will be initially pushed out as testing
in a few minutes time to check the autobuilders can't find anything.

Thanks,

Jonathan

> 
> Not supported: 
> 1. External Vref
> 2. Additional Configuration Modes
>         Temperature Sensor Mode: report temp data (not voltage).
> 
>         Line Frequency Rejection Mode: select to reject 50Hz or 60Hz
> 	or both. (both is default)
This is interesting... Will need some new ABI.  It's a filter so we probably
want to try and fit it in with the existing filter ABI.  
> 
>         Speed Mode: Default speed mode (1x) performs two conversions each
> 	cycle and combines the results.  2x speed mode only does one
> 	conversion each cycle.
Really simple case of oversampling.  So this one is easy ;)

> 3. Power management
> 4. DT Bindings
> 5. Triggered buffers
Device is really slow, so no real rush on this one.  Nice to have for
the convenience of using standard interfaces in libiio etc, but
at 7sps reading sysfs will work fine for all usecases!

> 6. What else?
Other power supply regulators..
(allows complete power disabling if there is an appropriate controllable
regulator on the board).

> 
> 
>  drivers/iio/adc/Kconfig   |   9 +++
>  drivers/iio/adc/Makefile  |   1 +
>  drivers/iio/adc/ltc2485.c | 146 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 156 insertions(+)
>  create mode 100644 drivers/iio/adc/ltc2485.c
> 
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 1de31bd..a042611 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -264,6 +264,15 @@ config LPC18XX_ADC
>  	  To compile this driver as a module, choose M here: the module will be
>  	  called lpc18xx_adc.
>  
> +config LTC2485
> +	tristate "Linear Technology LTC2485 ADC driver"
> +	depends on I2C
> +	help
> +	  Say yes here to build support for Linear Technology LTC2485 ADC.
> +
> +	  To compile this driver as a module, choose M here: the module will be
> +	  called ltc2485.
> +
>  config MAX1027
>  	tristate "Maxim max1027 ADC driver"
>  	depends on SPI
> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
> index 0ba0d50..1be5747 100644
> --- a/drivers/iio/adc/Makefile
> +++ b/drivers/iio/adc/Makefile
> @@ -27,6 +27,7 @@ obj-$(CONFIG_IMX7D_ADC) += imx7d_adc.o
>  obj-$(CONFIG_INA2XX_ADC) += ina2xx-adc.o
>  obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
>  obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
> +obj-$(CONFIG_LTC2485) += ltc2485.o
>  obj-$(CONFIG_MAX1027) += max1027.o
>  obj-$(CONFIG_MAX1363) += max1363.o
>  obj-$(CONFIG_MCP320X) += mcp320x.o
> diff --git a/drivers/iio/adc/ltc2485.c b/drivers/iio/adc/ltc2485.c
> new file mode 100644
> index 0000000..d8f9dac
> --- /dev/null
> +++ b/drivers/iio/adc/ltc2485.c
> @@ -0,0 +1,146 @@
> +/*
> + * ltc2485.c - Driver for Linear Technology LTC2485 ADC
> + *
> + * Copyright (C) 2016 Alison Schofield <amsfield22@gmail.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * Datasheet: http://cds.linear.com/docs/en/datasheet/2485fd.pdf
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +
> +/* Power-on configuration: rejects both 50/60Hz, operates at 1x speed */
> +#define LTC2485_CONFIG_DEFAULT		0
> +
> +struct ltc2485_data {
> +	struct i2c_client	*client;
> +	ktime_t			time_prev;	/* last conversion */
> +};
> +
> +static void ltc2485_wait_conv(struct ltc2485_data *data)
> +{
> +	const unsigned int conv_time = 147;	/* conversion time ms */
> +	unsigned int time_elapsed;
> +
> +	/* delay if conversion time not passed since last read or write */
> +	time_elapsed = ktime_ms_delta(ktime_get(), data->time_prev);
> +
> +	if (time_elapsed < conv_time)
> +		msleep(conv_time - time_elapsed);
> +}
> +
> +static int ltc2485_read(struct ltc2485_data *data, int *val)
> +{
> +	struct i2c_client *client = data->client;
> +	__be32 buf = 0;
> +	int ret;
> +
> +	ltc2485_wait_conv(data);
> +
> +	ret = i2c_master_recv(client, (char *)&buf, 4);
> +	if (ret < 0)  {
> +		dev_err(&client->dev, "i2c_master_recv failed\n");
> +		return ret;
> +	}
> +	data->time_prev = ktime_get();
> +	*val = sign_extend32(be32_to_cpu(buf) >> 6, 24);
Slightly preference for a blank line before a simple return statement like
this.  Makes it ever so slightly easier to read.
> +	return ret;
> +}
> +
> +static int ltc2485_read_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int *val, int *val2, long mask)
> +{
> +	struct ltc2485_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	if (mask == IIO_CHAN_INFO_RAW) {
> +		ret = ltc2485_read(data, val);
> +		if (ret < 0)
> +			return ret;
> +
> +		return IIO_VAL_INT;
> +
> +	} else if (mask == IIO_CHAN_INFO_SCALE) {
> +		*val = 5000;			/* on board vref millivolts */
> +		*val2 = 25;			/* 25 (24 + sign) data bits */
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +
> +	} else {
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_chan_spec ltc2485_channel[] = {
> +	{
> +		.type = IIO_VOLTAGE,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE)
> +	},
> +};
> +
> +static const struct iio_info ltc2485_info = {
> +	.read_raw = ltc2485_read_raw,
> +	.driver_module = THIS_MODULE,
> +};
> +
> +static int ltc2485_probe(struct i2c_client *client,
> +			 const struct i2c_device_id *id)
> +{
> +	struct iio_dev *indio_dev;
> +	struct ltc2485_data *data;
> +	int ret;
> +
> +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C |
> +				     I2C_FUNC_SMBUS_WRITE_BYTE))
> +		return -EOPNOTSUPP;
> +
> +	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);
> +	i2c_set_clientdata(client, indio_dev);
> +	data->client = client;
> +
> +	indio_dev->dev.parent = &client->dev;
> +	indio_dev->name = id->name;
> +	indio_dev->info = &ltc2485_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = ltc2485_channel;
> +	indio_dev->num_channels = ARRAY_SIZE(ltc2485_channel);
> +
> +	ret = i2c_smbus_write_byte(data->client, LTC2485_CONFIG_DEFAULT);
> +	if (ret < 0)
> +		return ret;
> +
> +	data->time_prev = ktime_get();
> +	return devm_iio_device_register(&client->dev, indio_dev);
> +}
> +
> +static const struct i2c_device_id ltc2485_id[] = {
> +	{ "ltc2485", 0 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, ltc2485_id);
> +
> +static struct i2c_driver ltc2485_driver = {
> +	.driver = {
> +		.name = "ltc2485",
> +	},
> +	.probe = ltc2485_probe,
> +	.id_table = ltc2485_id,
> +};
> +module_i2c_driver(ltc2485_driver);
> +
> +MODULE_AUTHOR("Alison Schofield <amsfield22@gmail.com>");
> +MODULE_DESCRIPTION("Linear Technology LTC2485 ADC driver");
> +MODULE_LICENSE("GPL v2");
> 

Re: [PATCH v2] iio: adc: ltc2485: add support for Linear Technology LTC2485 ADC

[Alison Schofield]

On Mon, Aug 29, 2016 at 05:01:14PM +0100, Jonathan Cameron wrote:
> On 25/08/16 06:48, Alison Schofield wrote:
> > Adds basic support for the LTC2485 ADC - a delta-sigma analog-to-digital
> > converter with an I2C interface that operates in single shot conversion
> > mode.
> > 
> > The driver supports an on board 5V reference and the power-on default
> > configuration which rejects both 50hz & 60hz line frequencies and
> > operates in 1x speed mode.
> > 
> > Signed-off-by: Alison Schofield <amsfield22@gmail.com>
> > Cc: Daniel Baluta <daniel.baluta@gmail.com>
> > ---
> > Changes in v2:
> >   - changed the wait conversion time function to use monotonic rather than
> >     real time and to use milliseconds rather than nanoseconds.  
> >   - made conv time a constant int.
> > 
> > Same notes as in v1:
> > Reviewers: In addition to commenting on what is present, please comment
> > on what is absent and the priority in which you would like to see
> > additional features added to this driver, or needed in this first submittal.
> None of the below are needed for initially submital.
> All 'value' add features at the end of the day. Job one: get reading from
> ADC done :)
> 
> I made a few really small white space changes and applied this to the
> togreg branch of iio.git.  Will be initially pushed out as testing
> in a few minutes time to check the autobuilders can't find anything.
> 
> Thanks,
> 
> Jonathan
> 
> > 
> > Not supported: 
> > 1. External Vref
> > 2. Additional Configuration Modes
> >         Temperature Sensor Mode: report temp data (not voltage).
> > 
> >         Line Frequency Rejection Mode: select to reject 50Hz or 60Hz
> > 	or both. (both is default)
> This is interesting... Will need some new ABI.  It's a filter so we probably
> want to try and fit it in with the existing filter ABI.  
> > 
> >         Speed Mode: Default speed mode (1x) performs two conversions each
> > 	cycle and combines the results.  2x speed mode only does one
> > 	conversion each cycle.
> Really simple case of oversampling.  So this one is easy ;)
> 
> > 3. Power management
> > 4. DT Bindings
> > 5. Triggered buffers
> Device is really slow, so no real rush on this one.  Nice to have for
> the convenience of using standard interfaces in libiio etc, but
> at 7sps reading sysfs will work fine for all usecases!
> 
> > 6. What else?
> Other power supply regulators..
> (allows complete power disabling if there is an appropriate controllable
> regulator on the board).
>
Thanks Jonathan!  
I need more direction on the power supply regulators. 

When you say power supply regulator, is that the same as reference
voltage?

The driver uses onboard vref now.  I see how I can add support for an
external vref.  But, it seems like maybe you are commenting that we can
have both, an external vref with an onboard vref as a fallback?  

Thanks,
alisons

Re: [PATCH v2] iio: adc: ltc2485: add support for Linear Technology LTC2485 ADC

[Jonathan Cameron]

On 02/09/16 20:15, Alison Schofield wrote:
> On Mon, Aug 29, 2016 at 05:01:14PM +0100, Jonathan Cameron wrote:
>> On 25/08/16 06:48, Alison Schofield wrote:
>>> Adds basic support for the LTC2485 ADC - a delta-sigma analog-to-digital
>>> converter with an I2C interface that operates in single shot conversion
>>> mode.
>>>
>>> The driver supports an on board 5V reference and the power-on default
>>> configuration which rejects both 50hz & 60hz line frequencies and
>>> operates in 1x speed mode.
>>>
>>> Signed-off-by: Alison Schofield <amsfield22@gmail.com>
>>> Cc: Daniel Baluta <daniel.baluta@gmail.com>
>>> ---
>>> Changes in v2:
>>>   - changed the wait conversion time function to use monotonic rather than
>>>     real time and to use milliseconds rather than nanoseconds.  
>>>   - made conv time a constant int.
>>>
>>> Same notes as in v1:
>>> Reviewers: In addition to commenting on what is present, please comment
>>> on what is absent and the priority in which you would like to see
>>> additional features added to this driver, or needed in this first submittal.
>> None of the below are needed for initially submital.
>> All 'value' add features at the end of the day. Job one: get reading from
>> ADC done :)
>>
>> I made a few really small white space changes and applied this to the
>> togreg branch of iio.git.  Will be initially pushed out as testing
>> in a few minutes time to check the autobuilders can't find anything.
>>
>> Thanks,
>>
>> Jonathan
>>
>>>
>>> Not supported: 
>>> 1. External Vref
>>> 2. Additional Configuration Modes
>>>         Temperature Sensor Mode: report temp data (not voltage).
>>>
>>>         Line Frequency Rejection Mode: select to reject 50Hz or 60Hz
>>> 	or both. (both is default)
>> This is interesting... Will need some new ABI.  It's a filter so we probably
>> want to try and fit it in with the existing filter ABI.  
>>>
>>>         Speed Mode: Default speed mode (1x) performs two conversions each
>>> 	cycle and combines the results.  2x speed mode only does one
>>> 	conversion each cycle.
>> Really simple case of oversampling.  So this one is easy ;)
>>
>>> 3. Power management
>>> 4. DT Bindings
>>> 5. Triggered buffers
>> Device is really slow, so no real rush on this one.  Nice to have for
>> the convenience of using standard interfaces in libiio etc, but
>> at 7sps reading sysfs will work fine for all usecases!
>>
>>> 6. What else?
>> Other power supply regulators..
>> (allows complete power disabling if there is an appropriate controllable
>> regulator on the board).
>>
> Thanks Jonathan!  
> I need more direction on the power supply regulators. 
> 
> When you say power supply regulator, is that the same as reference
> voltage?
> 
> The driver uses onboard vref now.  I see how I can add support for an
> external vref.  But, it seems like maybe you are commenting that we can
> have both, an external vref with an onboard vref as a fallback?  
Usual trick here is that if the external vref is wired, then it makes sense
to use it (or why would the hardware designer have put the source device
on the board!).  Hence we use regulator_get_optional call and handle the
not present response which would indicate that the optional devicetree
parameter or similar was not supplied - implying no hardware present.

So if it's not there we use the internal reference as currently doing.

Actually when I brought this up I meant the main power supply to
the chip.  On a lot of boards it makes sense to power down the regulators
when going to sleep etc and sometimes even during runtime.  To do that
we have to make the device aware of its regulators (including the
reference one if present).

Linus Waleij is someone who does this stuff right in his drivers, so
take a look at one of those.

Personally I've always counted this as a feature. If it's not there
then on boards where that powersupply is turned off the device won't
work, but there are plenty of boards with out fined grained enough
control where it doesn't matter.  If it's initially on adding this
support improves power saving.  Nice to have again, but not a requirement
for a driver to 'work'.

Jonathan
> 
> Thanks,
> alisons
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