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

[Guenter Roeck <guenter.roeck@ericsson.com>]

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. 

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. If so,
for the calculation to have any value, you might be better off using
DIV_ROUND_CLOSEST(val * scalepart, 1000000000L).

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 ?

> +	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" ?

Unless I am missing something, you only use st->attrs[0] ..
st->attrs[st->num_channels-1].

Thanks,
Guenter