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Date:	Mon, 14 Jul 2014 22:59:54 +0200 (CEST)
From:	Peter Meerwald <pmeerw@...erw.net>
To:	Philippe Reynes <tremyfr@...oo.fr>
cc:	Jonathan Cameron <jic23@...nel.org>, linux-iio@...r.kernel.org,
	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

Hello,

some more nitpicking inline below

regards, p.

> 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

DAC

> > +
> > +Optional properties:
> > +	- vref_mv: Reference input Voltage in mv. This should only be set if

voltage

> > +	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.

DAC maybe

> > +
> >   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;

indio_dev->name is not set

> > +
> > +	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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-- 

Peter Meerwald
+43-664-2444418 (mobile)
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