Message-ID: <5675865F.6050306@kernel.org>
Date:	Sat, 19 Dec 2015 16:31:27 +0000
From:	Jonathan Cameron <jic23@...nel.org>
To:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Hartmut Knaack <knaack.h@....de>,
	Peter Meerwald <pmeerw@...erw.net>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: add ad5761 DAC driver

On 16/12/15 13:27, Ricardo Ribalda Delgado wrote:
> ad5761 is a 1-channel DAC with configurable output range.
> The driver uses the regulator interface for its voltage ref.
> 
> It shares its register layout with ad5761r, ad5721 and ad5721r.
> 
> Differences:
> ad5761* are 16 bit, ad5721* are 12 bits.
> ad57*1r have an internal reference.
> 
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Mostly fine, but the range stuff is not standard ABI.  Whilst it is
rather fiddly to fit it to standard ABI it shouldn't be too bad.

A few other bits inline.

Jonathan
> ---
>  CREDITS                  |   1 +
>  drivers/iio/dac/Kconfig  |  10 ++
>  drivers/iio/dac/Makefile |   1 +
>  drivers/iio/dac/ad5761.c | 425 +++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 437 insertions(+)
>  create mode 100644 drivers/iio/dac/ad5761.c
> 
> diff --git a/CREDITS b/CREDITS
> index 8207cc62ee9d..44ea433d70a1 100644
> --- a/CREDITS
> +++ b/CREDITS
> @@ -3035,6 +3035,7 @@ D: PLX USB338x driver
>  D: PCA9634 driver
>  D: Option GTM671WFS
>  D: Fintek F81216A
> +D: AD5761 iio driver
>  D: Various kernel hacks
>  S: Qtechnology A/S
>  S: Valby Langgade 142
> diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
> index e701e28fb1cd..4caedd671360 100644
> --- a/drivers/iio/dac/Kconfig
> +++ b/drivers/iio/dac/Kconfig
> @@ -111,6 +111,16 @@ config AD5755
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called ad5755.
>  
> +config AD5761
> +	tristate "Analog Devices AD5761/61R/21/21R DAC driver"
> +	depends on SPI_MASTER
> +	help
> +	  Say yes here to build support for Analog Devices AD5761, AD5761R, AD5721,
> +	  AD5721R Digital to Analog Converter.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called ad5761.
> +
>  config AD5764
>  	tristate "Analog Devices AD5764/64R/44/44R DAC driver"
>  	depends on SPI_MASTER
> diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
> index 63ae05633e0c..cb525b53fc7b 100644
> --- a/drivers/iio/dac/Makefile
> +++ b/drivers/iio/dac/Makefile
> @@ -12,6 +12,7 @@ obj-$(CONFIG_AD5504) += ad5504.o
>  obj-$(CONFIG_AD5446) += ad5446.o
>  obj-$(CONFIG_AD5449) += ad5449.o
>  obj-$(CONFIG_AD5755) += ad5755.o
> +obj-$(CONFIG_AD5761) += ad5761.o
>  obj-$(CONFIG_AD5764) += ad5764.o
>  obj-$(CONFIG_AD5791) += ad5791.o
>  obj-$(CONFIG_AD5686) += ad5686.o
> diff --git a/drivers/iio/dac/ad5761.c b/drivers/iio/dac/ad5761.c
> new file mode 100644
> index 000000000000..b4eac59ef81f
> --- /dev/null
> +++ b/drivers/iio/dac/ad5761.c
> @@ -0,0 +1,425 @@
> +/*
> + * AD5721, AD5721R, AD5761, AD5761R, Voltage Output Digital to Analog Converter
> + *
> + * Copyright 2015 Qtechnology A/S
> + *
> + * Licensed under the GPL-2.
> + */
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/spi/spi.h>
> +#include <linux/bitops.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/regulator/consumer.h>
> +
> +#define AD5761_ADDR(addr)		((addr&0xf) << 16)
> +#define AD5761_ADDR_NOOP		0x0
> +#define AD5761_ADDR_DAC_WRITE		0x3
> +#define AD5761_ADDR_CTRL_WRITE_REG	0x4
> +#define AD5761_ADDR_SW_DATA_RESET	0x7
> +#define AD5761_ADDR_DAC_READ		0xb
> +#define AD5761_ADDR_CTRL_READ_REG	0xc
> +#define AD5761_ADDR_SW_FULL_RESET	0xf
> +
> +#define AD5761_CTRL_USE_INTVREF		BIT(5)
> +#define AD5761_CTRL_ETS			BIT(6)
> +
> +/**
> + * struct ad5761_chip_info - chip specific information
> + * @int_vref:	Value of the internal reference voltage in mV - 0 if external
> + *		reference voltage is used
> + * @channel	channel specification
> +*/
> +
> +struct ad5761_chip_info {
> +	unsigned long int_vref;
> +	const struct iio_chan_spec channel;
> +};
> +
> +struct ad5761_range_params {
> +	int m;
> +	int c;
> +};
> +
> +/**
> + * ad5761_supported_device_ids:
Single line comment syntax please.
> + */
> +
> +enum ad5761_supported_device_ids {
> +	ID_AD5721,
> +	ID_AD5721R,
> +	ID_AD5761,
> +	ID_AD5761R,
> +};
> +
> +/**
> + * struct ad5761_state - driver instance specific data
> + * @spi:		spi_device
> + * @chip_info:		chip model specific constants
> + * @vref_mv:		actual reference voltage used
> + */
> +struct ad5761_state {
> +	struct spi_device		*spi;
> +	struct regulator		*vref_reg;
> +
> +	bool use_intref;
> +	int vref;
> +	int range;
> +
> +	/*
> +	 * DMA (thus cache coherency maintenance) requires the
> +	 * transfer buffers to live in their own cache lines.
> +	 */
> +	union {
> +		__be32 d32;
> +		u8 d8[4];
> +	} data[3] ____cacheline_aligned;
> +};
> +
> +enum ad5761_range_ids {
> +	MODE_M10V_10V,
> +	MODE_0V_10V,
> +	MODE_M5V_5V,
> +	MODE_0V_5V,
> +	MODE_M2V5_7V5,
> +	MODE_M3V_3V,
> +	MODE_0V_16V,
> +	MODE_0V_20V,
> +};
> +
> +static const struct ad5761_range_params ad5761_range_params[] = {
> +	[MODE_M10V_10V] = {
> +		.m = 80,
> +		.c = 40,
> +	},
> +	[MODE_0V_10V] = {
> +		.m = 40,
> +		.c = 0,
> +	},
> +	[MODE_M5V_5V] = {
> +		.m = 40,
> +		.c = 20,
> +	},
> +	[MODE_0V_5V] = {
> +		.m = 20,
> +		.c = 0,
> +	},
> +	[MODE_M2V5_7V5] = {
> +		.m = 40,
> +		.c = 10,
> +	},
> +	[MODE_M3V_3V] = {
> +		.m = 24,
> +		.c = 12,
> +	},
> +	[MODE_0V_16V] = {
> +		.m = 64,
> +		.c = 0,
> +	},
> +	[MODE_0V_20V] = {
> +		.m = 80,
> +		.c = 0,
> +	},
> +};
> +
> +static const char * const ad5761_ranges[] = {
> +	[MODE_M10V_10V] = "-10V_10V",
> +	[MODE_0V_10V] = "0V_10V",
> +	[MODE_M5V_5V] = "-5V_5V",
> +	[MODE_0V_5V] = "0V_5V",
> +	[MODE_M2V5_7V5] = "-2V5_7V5",
> +	[MODE_M3V_3V] = "-3V_3V",
> +	[MODE_0V_16V] = "0V_16V",
> +	[MODE_0V_20V] = "0V_20V",
> +};
This is totally non standard ABI.  See below.
> +
> +static int ad5761_spi_write(struct ad5761_state *st, u8 addr, u16 val)
> +{
> +	st->data[0].d32 = cpu_to_be32(AD5761_ADDR(addr) | val);
> +
> +	return spi_write(st->spi, &st->data[0].d8[1], 3);
> +}
> +
> +static int ad5761_spi_read(struct ad5761_state *st, u8 addr, u16 *val)
> +{
> +	int ret;
> +	struct spi_transfer xfers[] = {
> +		{
> +			.tx_buf = &st->data[0].d8[1],
> +			.bits_per_word = 8,
> +			.len = 3,
> +			.cs_change = true,
> +		}, {
> +			.tx_buf = &st->data[1].d8[1],
> +			.rx_buf = &st->data[2].d8[1],
> +			.bits_per_word = 8,
> +			.len = 3,
> +		},
> +	};
> +
> +	st->data[0].d32 = cpu_to_be32(AD5761_ADDR(addr));
> +	st->data[1].d32 = cpu_to_be32(AD5761_ADDR(AD5761_ADDR_NOOP));
> +
> +	ret = spi_sync_transfer(st->spi, xfers, ARRAY_SIZE(xfers));
> +
> +	*val = be32_to_cpu(st->data[2].d32);
> +
> +	return ret;
> +}
> +
> +static int ad5761_spi_set_range(struct ad5761_state *st, int range)
> +{
> +	u16 aux;
> +	int ret;
> +
> +	aux = range;
> +	aux |= AD5761_CTRL_ETS;
> +	if (st->use_intref)
> +		aux |= AD5761_CTRL_USE_INTVREF;
A few blank lines in here would make this a touch more readable.
> +	ret = ad5761_spi_write(st, AD5761_ADDR_CTRL_WRITE_REG, aux);
> +	if (ret)
> +		return ret;
blank line here.
> +	ret = ad5761_spi_write(st, AD5761_ADDR_SW_DATA_RESET, 0);
> +	if (ret)
> +		return ret;
> +
> +	st->range = range;
blank line here.
> +	return 0;
> +}
> +
> +static int ad5761_read_raw(struct iio_dev *indio_dev,
> +			   struct iio_chan_spec const *chan,
> +			   int *val,
> +			   int *val2,
> +			   long m)
> +{
> +	struct ad5761_state *st = iio_priv(indio_dev);
> +	int ret;
> +	u16 aux;
> +
> +	switch (m) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = ad5761_spi_read(st, AD5761_ADDR_DAC_READ, &aux);
> +		if (ret)
> +			return ret;
> +		*val = aux >> chan->scan_type.shift;
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = st->vref * ad5761_range_params[st->range].m;
> +		*val /= 10;
> +		*val2 = chan->scan_type.realbits;
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +	case IIO_CHAN_INFO_OFFSET:
> +		*val = -(1<<chan->scan_type.realbits);
> +		*val *=	ad5761_range_params[st->range].c;
> +		*val /=	ad5761_range_params[st->range].m;
> +		return IIO_VAL_INT;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +}
> +
> +static int ad5761_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val,
> +			    int val2,
> +			    long mask)
> +{
> +	struct ad5761_state *st = iio_priv(indio_dev);
> +	u16 aux;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		aux =  val << chan->scan_type.shift;
> +		return ad5761_spi_write(st, AD5761_ADDR_DAC_WRITE, aux);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int ad5761_set_range(struct iio_dev *indio_dev,
> +	const struct iio_chan_spec *chan, unsigned int range)
> +{
> +	struct ad5761_state *st = iio_priv(indio_dev);
> +
> +	return ad5761_spi_set_range(st, range);
> +}
> +
> +static int ad5761_get_range(struct iio_dev *indio_dev,
> +	const struct iio_chan_spec *chan)
> +{
> +	struct ad5761_state *st = iio_priv(indio_dev);
> +	u16 aux;
> +	int ret;
> +
> +	ret = ad5761_spi_read(st, AD5761_ADDR_CTRL_READ_REG, &aux);
> +	if (ret)
> +		return ret;
> +
> +	return aux & 0x7;
> +}
> +
> +static const struct iio_info ad5761_info = {
> +	.read_raw = &ad5761_read_raw,
> +	.write_raw = &ad5761_write_raw,
> +	.driver_module = THIS_MODULE,
> +};
> +
> +static const struct iio_enum ad5761_range_enum = {
> +	.items = ad5761_ranges,
> +	.num_items = ARRAY_SIZE(ad5761_ranges),
> +	.get = ad5761_get_range,
> +	.set = ad5761_set_range,
> +};
> +
> +static struct iio_chan_spec_ext_info ad5761_ext_info[] = {
> +	IIO_ENUM("range", IIO_SHARED_BY_TYPE,
> +		 &ad5761_range_enum),
> +	IIO_ENUM_AVAILABLE("range", &ad5761_range_enum),
> +	{ },
> +};
Range isn't actually specified in the ABI docs.
Documenation\ABI\testing\sysfs-bus-iio*
The control interface for this is normally scale rather than range
(we had to pick one of the two and that is the way it fell out)  Usually
hardware designers care about range, but userspace programs are often
most directly interested in scale factors that need to be applied.
(and that was my most rediculously over generalized statement for the day ;)

I can see this is rather complex here given the random looking collection
of associated scales and offsets.  You would have to have _available
attributes to say what offsets are available at a given scale I think.
Also we'd have to then define a precedence order in the docs for the
two attributes (worth doing to make it obvious what to do when this
sort of setup arises).

> +
> +#define AD5761_CHAN(_bits) {				\
> +	.type = IIO_VOLTAGE,				\
> +	.output = 1,					\
> +	.indexed = 1,					\
> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),	\
> +	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |	\
> +		BIT(IIO_CHAN_INFO_OFFSET),		\
> +	.scan_type = {					\
> +		.sign = 'u',				\
> +		.realbits = (_bits),			\
> +		.storagebits = 16,			\
> +		.shift = 16 - (_bits),			\
> +	},						\
> +	.ext_info = ad5761_ext_info,			\
> +}
> +
> +static const struct ad5761_chip_info ad5761_chip_infos[] = {
> +	[ID_AD5721] = {
> +		.int_vref = 0,
> +		.channel = AD5761_CHAN(12),
> +	},
> +	[ID_AD5721R] = {
> +		.int_vref = 2500,
> +		.channel = AD5761_CHAN(12),
> +	},
> +	[ID_AD5761] = {
> +		.int_vref = 0,
> +		.channel = AD5761_CHAN(16),
> +	},
> +	[ID_AD5761R] = {
> +		.int_vref = 2500,
> +		.channel = AD5761_CHAN(16),
> +	},
> +};
> +
> +static void ad5761_get_vref(struct ad5761_state *st)
> +{
> +	int ret;
> +
> +
Single blank line only please.
> +	st->vref_reg = devm_regulator_get(&st->spi->dev, "vref");
> +	if (IS_ERR(st->vref_reg))
Don't eat errors that may be informative.
If it's optional, then use the get_optional calls, though care will be
needed as it's only sometimes optional here..
> +		return;
> +
> +	ret = regulator_enable(st->vref_reg);
> +	if (ret) {
> +		dev_warn(&st->spi->dev, "Failed to enable vref. Using internal");
> +		return;
> +	}
> +
> +	ret = regulator_get_voltage(st->vref_reg);
> +	if (ret < 0) {
> +		regulator_disable(st->vref_reg);
> +		dev_warn(&st->spi->dev,
> +			 "Failed to get vref value. Using internal");
> +		return;
> +	}
> +
> +	if (ret < 2000000 || ret > 3000000) {
> +		regulator_disable(st->vref_reg);
> +		dev_warn(&st->spi->dev,
> +				"Invalid external vref value. Using internal");
> +		return;
> +	}
> +
> +	st->vref = ret / 1000;
> +	st->use_intref = false;
> +}
> +
> +static int ad5761_probe(struct spi_device *spi)
> +{
> +	struct iio_dev *iio_dev;
> +	struct ad5761_state *st;
> +	int ret;
> +	const struct ad5761_chip_info *chip_info =
> +		&ad5761_chip_infos[spi_get_device_id(spi)->driver_data];
> +
> +	iio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
> +	if (!iio_dev)
> +		return -ENOMEM;
> +	st = iio_priv(iio_dev);
> +
> +	st->spi = spi;
> +	spi_set_drvdata(spi, iio_dev);
> +
> +	st->use_intref = true;
> +	st->vref = chip_info->int_vref;
> +	ad5761_get_vref(st);
> +	if (st->use_intref && !chip_info->int_vref) {
> +		dev_err(&spi->dev, "Missing vref, cannot continue");
> +		return -EIO;
> +	}
> +
> +	ad5761_spi_set_range(st, MODE_0V_5V);
> +
> +	iio_dev->dev.parent = &spi->dev;
> +	iio_dev->info = &ad5761_info;
> +	iio_dev->modes = INDIO_DIRECT_MODE;
> +	iio_dev->channels = &chip_info->channel;
> +	iio_dev->num_channels = 1;
> +	iio_dev->name = spi_get_device_id(st->spi)->name;
> +	ret = iio_device_register(iio_dev);
> +	if (ret && !IS_ERR(st->vref_reg))

I would ever so slightly prefer to have a matched funcitonto get_vref
(release_vref perhaps) so that it's obvious what this disable is
'undoing'.  At first glance, I wondered where it was being enabled!

> +		regulator_disable(st->vref_reg);
> +
> +	return ret;
> +}
> +
> +static int ad5761_remove(struct spi_device *spi)
> +{
> +	struct iio_dev *iio_dev = spi_get_drvdata(spi);
> +	struct ad5761_state *st = iio_priv(iio_dev);
> +
> +	if (!IS_ERR(st->vref_reg))
> +		regulator_disable(st->vref_reg);
> +	iio_device_unregister(iio_dev);
Nitpick.  Blank line before simple returns like this slightly
improves readability.

> +	return 0;
> +}
> +
> +static const struct spi_device_id ad5761_id[] = {
> +	{"ad5721", ID_AD5721},
> +	{"ad5721r", ID_AD5721R},
> +	{"ad5761", ID_AD5761},
> +	{"ad5761r", ID_AD5761R},
> +	{}
> +};
> +MODULE_DEVICE_TABLE(spi, ad5761_id);
> +
> +static struct spi_driver ad5761_driver = {
> +	.driver = {
> +		   .name = "ad5761",
> +		   .owner = THIS_MODULE,
> +		   },
> +	.probe = ad5761_probe,
> +	.remove = ad5761_remove,
> +	.id_table = ad5761_id,
> +};
> +module_spi_driver(ad5761_driver);
> +
> +MODULE_AUTHOR("Ricardo Ribalda <ricardo.ribalda@...il.com>");
> +MODULE_DESCRIPTION("Analog Devices AD5721, AD5721R, AD5761, AD5761R driver");
> +MODULE_LICENSE("GPL v2");
> 

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