Re: [PATCH 5/6] IIO:hwmon interface client driver.

[Jonathan Cameron <jic23@cam.ac.uk>]

On 10/20/11 16:12, Guenter Roeck wrote:
> On Thu, 2011-10-20 at 05:33 -0400, Jonathan Cameron wrote:
>> Should move to drivers/hwmon once people are happy with it.
>>
>> Minimal support of simple in, curr and temp attributes
>> so far.
>>
>> Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
>> ---
>>  drivers/iio/Kconfig     |    8 ++
>>  drivers/iio/Makefile    |    1 +
>>  drivers/iio/iio_hwmon.c |  227 +++++++++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 236 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
>> index 308bc97..c2f0970 100644
>> --- a/drivers/iio/Kconfig
>> +++ b/drivers/iio/Kconfig
>> @@ -11,6 +11,14 @@ menuconfig IIO
>>  
>>  if IIO
>>  
>> +config IIO_HWMON
>> +       tristate "Hwmon driver that uses channels specified via iio maps"
>> +       depends on HWMON
>> +       help
>> +	  This is a platform driver that in combination with a suitable
>> +	  map allows IIO devices to provide  basic hwmon functionality
>> +	  for those channels specified in the map.
>> +
>>  source "drivers/iio/adc/Kconfig"
>>  source "drivers/iio/imu/Kconfig"
>>  source "drivers/iio/light/Kconfig"
>> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
>> index cfb588a..5f9c01a 100644
>> --- a/drivers/iio/Makefile
>> +++ b/drivers/iio/Makefile
>> @@ -6,6 +6,7 @@ obj-y = inkern.o
>>  obj-$(CONFIG_IIO) += iio.o
>>  industrialio-y := core.o
>>  
>> +obj-$(CONFIG_IIO_HWMON) += iio_hwmon.o
>>  obj-y += adc/
>>  obj-y += imu/
>>  obj-y += light/
>> diff --git a/drivers/iio/iio_hwmon.c b/drivers/iio/iio_hwmon.c
>> new file mode 100644
>> index 0000000..b3348ad
>> --- /dev/null
>> +++ b/drivers/iio/iio_hwmon.c
>> @@ -0,0 +1,227 @@
>> +/* Hwmon client for industrial I/O devices
>> + *
>> + * Copyright (c) 2011 Jonathan Cameron
>> + *
>> + * 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.
>> + *
>> + * Limited functionality currently supported.
> 
> Just nitpicking ... this comment doesn't provide much value. It doesn't
> explain the limits, nor what could be improved.
> 
>> + */
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/slab.h>
>> +#include <linux/module.h>
>> +#include <linux/err.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/iio/inkern.h>
>> +#include <linux/hwmon.h>
>> +#include <linux/hwmon-sysfs.h>
>> +
>> +/**
>> + * struct iio_hwmon_state - device instance state
>> + * @channels:		filled with null terminated array of channels from iio
>> + * @num_channels:	number of channels in channels (saves counting twice)
>> + * @hwmon_dev:		associated hwmon device
>> + * @attr_group:	the group of attributes
>> + * @attrs:		null terminated array of attribute pointers.
>> + */
>> +struct iio_hwmon_state {
>> +	struct iio_channel **channels;
>> +	int num_channels;
>> +	struct device *hwmon_dev;
>> +	struct attribute_group attr_group;
>> +	struct attribute **attrs;
>> +};
>> +
>> +/*
>> + * Assumes that IIO and hwmon operate in the same base units.
>> + * This is supposed to be true, but needs verification for
>> + * new channel types.
>> + */
>> +static ssize_t iio_hwmon_read_val(struct device *dev,
>> +				  struct device_attribute *attr,
>> +				  char *buf)
>> +{
>> +	long result;
>> +	int val, ret, scaleint, scalepart;
>> +	struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr);
>> +	struct iio_hwmon_state *state = dev_get_drvdata(dev);
>> +
>> +	/*
>> +	 * No locking between this pair, so theoretically possible
>> +	 * the scale has changed.
>> +	 */
>> +	ret = iio_read_channel_raw(state->channels[sattr->index],
>> +				   &val);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	ret = iio_read_channel_scale(state->channels[sattr->index],
>> +				     &scaleint, &scalepart);
>> +	if (ret < 0)
>> +		return ret;
>> +	switch (ret) {
>> +	case IIO_VAL_INT:
>> +		result = val * scaleint;
>> +		break;
>> +	case IIO_VAL_INT_PLUS_MICRO:
>> +		result = (long)val * (long)scaleint +
>> +			(long)val * (long)scalepart / 1000000L;
>> +		break;
>> +	case IIO_VAL_INT_PLUS_NANO:
>> +		result = (long)val * (long)scaleint +
>> +			(long)val * (long)scalepart / 1000000000L;
>> +		break;
> 
> Still easy to imagine that val * scalepart gets larger than 2147483647L
> (on machines where sizeof(long) = 4) ... it will already happen if the
> result of (val * scalepart / 1000000000) is larger than 2. 
Good point.  I really ought to have done the calcs.
If we have maximum possible value in here things will be ugly.

Worst case is scalepart is 9999999999. (could be done as 1 - 0.000000001
which would be nicer, but we don't specify a preference - from this
discussion I am suspecting we should!)

Looks like 64 bits is going to be a requirement as you say.
> 
> What value range do you expect to see here ?
> 
> If (val * scaleint) is already the milli-unit, scalepart would possibly
> only address fractions of milli-units. If so, the result of (val *
> scalepart / 1000000000L) might always be smaller than 1, ie 0. 
It certainly should be.
> If so, for the calculation to have any value, you might be better off using
> DIV_ROUND_CLOSEST(val * scalepart, 1000000000L).
Good idea.
> 
> I am a bit confused by this anyway. Since hwmon in general reports
> milli-units, VAL_INT appears to reflect milli-units, VAL_INT_PLUS_MICRO
> really means nano-units, and IIO_VAL_INT_PLUS_NANO really means
> pico-units. Is this correct ?
Micro units of the scale factor.

Take my test part a max1363...
Scale is actually 0.5 so each adc count (e.g. raw value) is 0.5millivolts.

scale int here is 0,
scale part is 500,000 (so 0.5) and it returns IIO_VAL_INT_PLUS_MICRO.


> 
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +	return sprintf(buf, "%ld\n", result);
>> +}
>> +
>> +static void iio_hwmon_free_attrs(struct iio_hwmon_state *st)
>> +{
>> +	int i;
>> +	struct sensor_device_attribute *a;
>> +	for (i = 0; i < st->num_channels; i++)
>> +		if (st->attrs[i]) {
>> +			a = to_sensor_dev_attr(
>> +				container_of(st->attrs[i],
>> +					     struct device_attribute,
>> +					     attr));
>> +			kfree(a);
>> +		}
>> +}
>> +
>> +static int __devinit iio_hwmon_probe(struct platform_device *pdev)
>> +{
>> +	struct iio_hwmon_state *st;
>> +	struct sensor_device_attribute *a;
>> +	int ret, i;
>> +	int in_i = 1, temp_i = 1, curr_i = 1;
>> +
>> +	st = kzalloc(sizeof(*st), GFP_KERNEL);
>> +	if (st == NULL) {
>> +		ret = -ENOMEM;
>> +		goto error_ret;
>> +	}
>> +
>> +	st->channels = iio_channel_get_all(&pdev->dev, NULL);
>> +	if (IS_ERR(st->channels)) {
>> +		ret = PTR_ERR(st->channels);
>> +		goto error_free_state;
>> +	}
>> +
>> +	/* count how many attributes we have */
>> +	while (st->channels[st->num_channels])
>> +		st->num_channels++;
>> +
>> +	st->attrs = kzalloc(sizeof(st->attrs) * (st->num_channels + 1),
>> +			    GFP_KERNEL);
> 
> Why "+ 1" ?
Null terminated list for attribute groups.  Hence the kzalloc.
> 
> Unless I am missing something, you only use st->attrs[0] ..
> st->attrs[st->num_channels-1].
> 
> Thanks,
> Guenter
> 
> 
>