Date:	Mon, 14 Jul 2014 21:21:42 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Philippe Reynes <tremyfr@...oo.fr>, linux-iio@...r.kernel.org
CC:	linux-kernel@...r.kernel.org, armadeus-forum@...ts.sourceforge.net,
	devicetree@...r.kernel.org, julien.boibessot@...e.fr
Subject: Re: [PATCH] iio: add support of the max5821

On 14/07/14 18:32, Philippe Reynes wrote:
> Signed-off-by: Philippe Reynes <tremyfr@...oo.fr>
Hi Philippe,

Mostly looks good, a few things inline.
Bigger ones are:
1) You need locking to prevent some state changes occuring mid way through a
    read (as it requires a register write then a read back of a value).
2) Use a regulator for your reference voltage.  We probably still have a few
    IIO drivers specifying references in a similar fashion to what you have
    here, but they are all ancient (and some predate the regulator framework).

Jonathan
> ---
>   .../devicetree/bindings/iio/dac/max5821.txt        |   18 +
>   drivers/iio/dac/Kconfig                            |    8 +
>   drivers/iio/dac/Makefile                           |    1 +
>   drivers/iio/dac/max5821.c                          |  368 ++++++++++++++++++++
>   4 files changed, 395 insertions(+), 0 deletions(-)
>   create mode 100644 Documentation/devicetree/bindings/iio/dac/max5821.txt
>   create mode 100644 drivers/iio/dac/max5821.c
>
> diff --git a/Documentation/devicetree/bindings/iio/dac/max5821.txt b/Documentation/devicetree/bindings/iio/dac/max5821.txt
> new file mode 100644
> index 0000000..242265f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/dac/max5821.txt
> @@ -0,0 +1,18 @@
> +Maxim max5821 DAC device driver
> +
> +Required properties:
> +	- compatible: Must be "maxim,max5821"
> +	- reg: Should contain the ADC I2C address
> +
> +Optional properties:
> +	- vref_mv: Reference input Voltage in mv. This should only be set if
> +	there is an external reference voltage connected to the REF
> +	pin. If the property is not set, 3600 is used as the reference voltage.
As stated below, this wants to be a regulator and you don't want to have
an arbitary default (just confuses matters).

> +
> +Example:
> +
> +	max5821@38 {
> +		compatible = "maxim,max5821";
> +		reg = <0x38>;
> +		vref_mv = <3600>;
> +	};
> diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
> index f378ca8..4428acb 100644
> --- a/drivers/iio/dac/Kconfig
> +++ b/drivers/iio/dac/Kconfig
> @@ -152,6 +152,14 @@ config MAX517
>   	  This driver can also be built as a module.  If so, the module
>   	  will be called max517.
>
> +config MAX5821
> +	tristate "Maxim MAX5821 DAC driver"
> +	depends on I2C
> +	depends on OF
> +	help
> +	  Say yes here to build support for Maxim MAX5821
> +	  10 bits dac.
> +
>   config MCP4725
>   	tristate "MCP4725 DAC driver"
>   	depends on I2C
> diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
> index bb84ad6..82545c0 100644
> --- a/drivers/iio/dac/Makefile
> +++ b/drivers/iio/dac/Makefile
> @@ -17,4 +17,5 @@ obj-$(CONFIG_AD5791) += ad5791.o
>   obj-$(CONFIG_AD5686) += ad5686.o
>   obj-$(CONFIG_AD7303) += ad7303.o
>   obj-$(CONFIG_MAX517) += max517.o
> +obj-$(CONFIG_MAX5821) += max5821.o
>   obj-$(CONFIG_MCP4725) += mcp4725.o
> diff --git a/drivers/iio/dac/max5821.c b/drivers/iio/dac/max5821.c
> new file mode 100644
> index 0000000..92a1aa3
> --- /dev/null
> +++ b/drivers/iio/dac/max5821.c
> @@ -0,0 +1,368 @@
> + /*
> +  * iio/dac/max5821.c
> +  * Copyright (C) 2014 Philippe Reynes
> +  *
> +  * 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.
> +  */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/i2c.h>
> +#include <linux/iio/iio.h>
> +
> +#define MAX5821_DRV_NAME			"max5821"
I normally get slightly iritated with this convention.  In this case
you don't even use the above define.  Please get rid of it!

> +#define MAX5821_MAX_DAC_CHANNELS		2

> +
> +/* command bytes */
> +#define MAX5821_LOAD_DAC_A_IN_REG_B		0x00
> +#define MAX5821_LOAD_DAC_B_IN_REG_A		0x10
> +#define MAX5821_EXTENDED_COMMAND_MODE		0xf0
> +#define MAX5821_READ_DAC_A_COMMAND		0xf1
> +#define MAX5821_READ_DAC_B_COMMAND		0xf2
> +
> +#define MAX5821_EXTENDED_POWER_UP		0x00
> +#define MAX5821_EXTENDED_POWER_DOWN_MODE0	0x01
> +#define MAX5821_EXTENDED_POWER_DOWN_MODE1	0x02
> +#define MAX5821_EXTENDED_POWER_DOWN_MODE2	0x03
> +#define MAX5821_EXTENDED_DAC_A			0x04
> +#define MAX5821_EXTENDED_DAC_B			0x08
> +
> +enum max5821_device_ids {
> +	ID_MAX5821,
> +};
> +
> +struct max5821_data {
> +	struct i2c_client	*client;
> +	unsigned short		vref_mv;
> +	bool			powerdown[MAX5821_MAX_DAC_CHANNELS];
> +	u8			powerdown_mode[MAX5821_MAX_DAC_CHANNELS];
> +};
> +
> +static const char * const max5821_powerdown_modes[] = {
> +	"three_state",
> +	"1kohm_to_gnd",
> +	"100kohm_to_gnd",
> +};
> +
> +static int max5821_get_powerdown_mode(struct iio_dev *indio_dev,
> +				      const struct iio_chan_spec *chan)
> +{
> +	struct max5821_data *st = iio_priv(indio_dev);
> +
> +	return st->powerdown_mode[chan->channel];
> +}
> +
> +static int max5821_set_powerdown_mode(struct iio_dev *indio_dev,
> +				      const struct iio_chan_spec *chan,
> +				      unsigned int mode)
> +{
> +	struct max5821_data *st = iio_priv(indio_dev);
> +
> +	st->powerdown_mode[chan->channel] = mode;
> +
> +	return 0;
> +}
> +
> +static const struct iio_enum max5821_powerdown_mode_enum = {
> +	.items = max5821_powerdown_modes,
> +	.num_items = ARRAY_SIZE(max5821_powerdown_modes),
> +	.get = max5821_get_powerdown_mode,
> +	.set = max5821_set_powerdown_mode,
> +};
> +
> +static ssize_t max5821_read_dac_powerdown(struct iio_dev *indio_dev,
> +					  uintptr_t private,
> +					  const struct iio_chan_spec *chan,
> +					  char *buf)
> +{
> +	struct max5821_data *st = iio_priv(indio_dev);
> +
> +	return sprintf(buf, "%d\n", st->powerdown[chan->channel]);
> +}
> +
> +static int max5821_sync_powerdown_mode(struct max5821_data *data,
> +				       const struct iio_chan_spec *chan)
> +{
> +	u8 outbuf[2];
> +
> +	outbuf[0] = MAX5821_EXTENDED_COMMAND_MODE;
> +
> +	if (chan->channel == 0)
> +		outbuf[1] = MAX5821_EXTENDED_DAC_A;
> +	else
> +		outbuf[1] = MAX5821_EXTENDED_DAC_B;
> +
> +	if (data->powerdown[chan->channel])
> +		outbuf[1] |= data->powerdown_mode[chan->channel] + 1;
> +	else
> +		outbuf[1] |= MAX5821_EXTENDED_POWER_UP;
> +
> +	return i2c_master_send(data->client, outbuf, 2);
> +}
> +
> +static ssize_t max5821_write_dac_powerdown(struct iio_dev *indio_dev,
> +					   uintptr_t private,
> +					   const struct iio_chan_spec *chan,
> +					   const char *buf, size_t len)
> +{
> +	struct max5821_data *data = iio_priv(indio_dev);
> +	bool powerdown;
> +	int ret;
> +
> +	ret = strtobool(buf, &powerdown);
> +	if (ret)
> +		return ret;
> +
> +	data->powerdown[chan->channel] = powerdown;
> +
> +	ret = max5821_sync_powerdown_mode(data, chan);
> +	if (ret < 0)
> +		return ret;
> +
> +	return len;
> +}
> +
> +static const struct iio_chan_spec_ext_info max5821_ext_info[] = {
> +	{
> +		.name = "powerdown",
> +		.read = max5821_read_dac_powerdown,
> +		.write = max5821_write_dac_powerdown,
> +		.shared = IIO_SEPARATE,
> +	},
> +	IIO_ENUM("powerdown_mode", IIO_SEPARATE, &max5821_powerdown_mode_enum),
> +	IIO_ENUM_AVAILABLE("powerdown_mode", &max5821_powerdown_mode_enum),
> +	{ },
> +};
> +
> +#define MAX5821_CHANNEL(chan) {					\
> +	.type = IIO_VOLTAGE,					\
> +	.indexed = 1,						\
> +	.output = 1,						\
> +	.channel = (chan),					\
> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> +	.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SCALE),	\
> +	.ext_info = max5821_ext_info,				\
> +}
> +
> +static const struct iio_chan_spec max5821_channels[] = {
> +	MAX5821_CHANNEL(0),
> +	MAX5821_CHANNEL(1)
> +};
> +
> +static int max5821_get_value(struct iio_dev *indio_dev,
> +			     int *val, int channel)
> +{
> +	struct max5821_data *data = iio_priv(indio_dev);
> +	struct i2c_client *client = data->client;
> +	u8 outbuf[1];
> +	u8 inbuf[2];
> +	int ret;
> +
> +	switch (channel) {
> +	case 0:
> +		outbuf[0] = MAX5821_READ_DAC_A_COMMAND;
> +		break;
> +	case 1:
> +		outbuf[0] = MAX5821_READ_DAC_B_COMMAND;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	ret = i2c_master_send(client, outbuf, 1);
> +	if (ret < 0)
> +		return ret;
> +	else if (ret != 1)
> +		return -EIO;
> +
> +	ret = i2c_master_recv(client, inbuf, 2);
> +	if (ret < 0)
> +		return ret;
> +	else if (ret != 2)
> +		return -EIO;
It somehow always feels like this error handling should be in the
i2c core.  Just how often does it make sense to receive too little
from and i2c transaction?  Anyhow, such is life ;)
You could set this up to use i2c_transfer instead of separating it like
this.
You also have no locking in here so it's more than possible that two
simultaneous reads will occur messing up what you get back.
(add a mutex around all cases where a change in the middle of a function
  might mess things up).
> +
> +	*val = ((inbuf[0] & 0x0f) << 6) | (inbuf[1] >> 2);
> +
> +	return IIO_VAL_INT;
> +}
> +
> +static int max5821_set_value(struct iio_dev *indio_dev,
> +			     int val, int channel)
> +{
> +	struct max5821_data *data = iio_priv(indio_dev);
> +	struct i2c_client *client = data->client;
> +	u8 outbuf[2];
> +	int ret;
> +
> +	if ((val < 0) || (val > 1023))
> +		return -EINVAL;
> +
> +	switch (channel) {
> +	case 0:
I would use a lookup table for these and other registers
thus moving the switch statements into a lookup in a table.
> +		outbuf[0] = MAX5821_LOAD_DAC_A_IN_REG_B;
> +		break;
> +	case 1:
> +		outbuf[0] = MAX5821_LOAD_DAC_B_IN_REG_A;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	outbuf[0] |= val >> 6;
> +	outbuf[1] = (val & 0x3f) << 2;
> +
> +	ret = i2c_master_send(client, outbuf, 2);
> +	if (ret < 0)
> +		return ret;
> +	else if (ret != 2)
> +		return -EIO;
> +	else
> +		return 0;
> +}
> +
> +static int max5821_read_raw(struct iio_dev *indio_dev,
> +			   struct iio_chan_spec const *chan,
> +			   int *val, int *val2, long mask)
> +{
> +	struct max5821_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = max5821_get_value(indio_dev, val, chan->channel);
return directly for simpler program flow and to loose the local
variable ret
> +		break;
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = data->vref_mv;
> +		*val2 = 10;
> +		ret = IIO_VAL_FRACTIONAL_LOG2;
> +		break;
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +static int max5821_write_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan,
> +			     int val, int val2, long mask)
> +{
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = max5821_set_value(indio_dev, val, chan->channel);
return directly to simplify the flow rather than waiting till the end
of the function.  Gets rid of the local variable ret as well.

Also you should verify that val2 = 0 to confirm valid inputs.
> +		break;
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +#ifdef CONFIG_PM_SLEEP
> +static int max5821_suspend(struct device *dev)
> +{
> +	u8 outbuf[2];
> +
> +	outbuf[0] = MAX5821_EXTENDED_COMMAND_MODE;
> +	outbuf[1] = MAX5821_EXTENDED_DAC_A | MAX5821_EXTENDED_DAC_B
> +				| MAX5821_EXTENDED_POWER_DOWN_MODE2;
> +
> +	return i2c_master_send(to_i2c_client(dev), outbuf, 2);
> +}
> +
> +static int max5821_resume(struct device *dev)
> +{
> +	u8 outbuf[2];
> +
> +	outbuf[0] = MAX5821_EXTENDED_COMMAND_MODE;
> +	outbuf[1] = MAX5821_EXTENDED_DAC_A | MAX5821_EXTENDED_DAC_B
> +				| MAX5821_EXTENDED_POWER_UP;
Perhaps use c99 array assignment
	u8 outbuf[2] = { MAX5821...

> +
> +	return i2c_master_send(to_i2c_client(dev), outbuf, 2);
> +}
> +
> +static SIMPLE_DEV_PM_OPS(max5821_pm_ops, max5821_suspend, max5821_resume);
> +#define MAX5821_PM_OPS (&max5821_pm_ops)
> +#else
> +#define MAX5821_PM_OPS NULL
> +#endif /* CONFIG_PM_SLEEP */
> +
> +static const struct iio_info max5821_info = {
> +	.read_raw = max5821_read_raw,
> +	.write_raw = max5821_write_raw,
> +	.driver_module = THIS_MODULE,
> +};
> +
> +static int max5821_probe(struct i2c_client *client,
> +			const struct i2c_device_id *id)
> +{
> +	struct max5821_data *data;
> +	struct iio_dev *indio_dev;
> +	struct device_node *np = client->dev.of_node;
> +	u32 tmp;
> +
> +	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;
> +
> +	/* max5821 start in powerdown mode 100Kohm to ground */
> +	for (tmp = 0; tmp < MAX5821_MAX_DAC_CHANNELS; tmp++) {
> +		data->powerdown[tmp] = 1;
It's a boolean so please use true or false
> +		data->powerdown_mode[tmp] = 2; /* index of "100kohm_to_gnd" */
Deploy defines to give magic values names, or in this case an actual enum
might make sense.
> +	}
> +
> +	if (of_property_read_u32(np, "vref_mv", &tmp) == 0)
> +		data->vref_mv = tmp;
> +	else
> +		data->vref_mv = 3600;
Please use a regulator for the voltage reference and don't provide a default
as there isn't any meaningful fall back (such as an internal reference).
> +
> +	indio_dev->dev.parent = &client->dev;
> +	indio_dev->num_channels = 2;
Apply the principal of saving reviewers looking elsewhere to
check anything. In this case use ARRAY_SIZE(max5821_channels) rather
than 2.
> +	indio_dev->channels = max5821_channels;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->info = &max5821_info;
> +
> +	return iio_device_register(indio_dev);
> +}
> +
> +static int max5821_remove(struct i2c_client *client)
> +{
> +	iio_device_unregister(i2c_get_clientdata(client));
As this is all that is in here, you can use devm_iio_device_register
and not have any remove function at all.  If you don't do it I'll
only get a patch sometime soon proposing the change :(

> +	return 0;
> +}
> +
> +static const struct i2c_device_id max5821_id[] = {
> +	{ "max5821", ID_MAX5821 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, max5821_id);
> +
> +static const struct of_device_id max5821_of_match[] = {
> +	{ .compatible = "maxim,max5821" },
> +	{ }
> +};
> +
> +static struct i2c_driver max5821_driver = {
> +	.driver = {
> +		.name	= "max5821",
> +		.pm     = MAX5821_PM_OPS,
> +		.owner	= THIS_MODULE,
> +	},
> +	.probe		= max5821_probe,
> +	.remove		= max5821_remove,
> +	.id_table	= max5821_id,
> +};
> +module_i2c_driver(max5821_driver);
> +
> +MODULE_AUTHOR("Philippe Reynes <tremyfr@...oo.fr>");
> +MODULE_DESCRIPTION("MAX5821 DAC");
> +MODULE_LICENSE("GPL v2");
>

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