Re: [PATCH 01/18] iio: Add helper functions for enum style channel attributes

[Jonathan Cameron <jic23@kernel.org>]

On 05/21/2012 12:42 PM, Lars-Peter Clausen wrote:
> We often have the case were we do have a enum style channel attribute. These
> attributes have in common that they are a list of string values which usually
> map in a 1-to-1 fashion to integer values.
> 
> This patch implements some common helper code for implementing enum style
> channel attributes using extended channel attributes. The helper functions take
> care of converting between the string and integer values, as well providing a
> function for "_available" attributes which list all available enum items.
> 
One trivial suggestion to mention the integers are unsigned inline...
It's kind of obvious but never hurts to hammer the point home!

> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
> 
> ---
> Changes since v1:
> 	* Add documentation for struct iio_enum, IIO_ENUM and IIO_ENUM_AVAILABLE.
> 	* Make set and get callbacks optional
> 
> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
> ---
>  drivers/iio/industrialio-core.c |   63 ++++++++++++++++++++++++++++++++++++++
>  include/linux/iio/iio.h         |   64 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 127 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 1ddd886..56a3c0b 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -289,6 +289,69 @@ static ssize_t iio_write_channel_ext_info(struct device *dev,
>  			       this_attr->c, buf, len);
>  }
>  
> +ssize_t iio_enum_available_read(struct iio_dev *indio_dev,
> +	uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
> +{
> +	const struct iio_enum *e = (const struct iio_enum *)priv;
> +	unsigned int i;
> +	size_t len = 0;
> +
> +	if (!e->num_items)
> +		return 0;
> +
> +	for (i = 0; i < e->num_items; ++i)
> +		len += snprintf(buf + len, PAGE_SIZE - len, "%s ", e->items[i]);
> +
> +	/* replace last space with a newline */
> +	buf[len - 1] = '\n';
> +
> +	return len;
> +}
> +EXPORT_SYMBOL_GPL(iio_enum_available_read);
> +
> +ssize_t iio_enum_read(struct iio_dev *indio_dev,
> +	uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
> +{
> +	const struct iio_enum *e = (const struct iio_enum *)priv;
> +	int i;
> +
> +	if (!e->get)
> +		return -EINVAL;
> +
> +	i = e->get(indio_dev, chan);
> +	if (i < 0)
> +		return i;
> +	else if (i >= e->num_items)
> +		return -EINVAL;
> +
> +	return sprintf(buf, "%s\n", e->items[i]);
> +}
> +EXPORT_SYMBOL_GPL(iio_enum_read);
> +
> +ssize_t iio_enum_write(struct iio_dev *indio_dev,
> +	uintptr_t priv, const struct iio_chan_spec *chan, const char *buf,
> +	size_t len)
> +{
> +	const struct iio_enum *e = (const struct iio_enum *)priv;
> +	unsigned int i;
> +	int ret;
> +
> +	if (!e->set)
> +		return -EINVAL;
> +
> +	for (i = 0; i < e->num_items; i++) {
> +		if (sysfs_streq(buf, e->items[i]))
> +			break;
> +	}
> +
> +	if (i == e->num_items)
> +		return -EINVAL;
> +
> +	ret = e->set(indio_dev, chan, i);
> +	return ret ? ret : len;
> +}
> +EXPORT_SYMBOL_GPL(iio_enum_write);
> +
>  static ssize_t iio_read_channel_info(struct device *dev,
>  				     struct device_attribute *attr,
>  				     char *buf)
> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
> index 3a4f6a3..7378bbd 100644
> --- a/include/linux/iio/iio.h
> +++ b/include/linux/iio/iio.h
> @@ -130,6 +130,70 @@ struct iio_chan_spec_ext_info {
>  };
>  
>  /**
> + * struct iio_enum - Enum channel info attribute
> + * items: A array of strings.
> + * num_items: Length of the item array.
> + * set: Set callback function, may be NULL.
> + * get: Get callback function, may be NULL.
> + *
> + * The iio_enum struct can be used to implement enum style channel attributes.
> + * Enum style attributes are those which have a set of strings which map to
> + * integer values. The IIO enum helper code takes care of mapping between the
> + * integer
Trivial but they are restricted to unsigned integers by the set interface.
 and string values as well as generating a "_available" file which
> + * contains a list of all available items. The set callback will be called when
> + * the attribute is updated. The last parameter is the index to the newly
> + * activated item. The get callback will be used to query the currently active
> + * item and is supposed to return the index for it.
> + */
> +struct iio_enum {
> +	const char * const *items;
> +	unsigned int num_items;
> +	int (*set)(struct iio_dev *, const struct iio_chan_spec *, unsigned int);
> +	int (*get)(struct iio_dev *, const struct iio_chan_spec *);
> +};
> +
> +ssize_t iio_enum_available_read(struct iio_dev *indio_dev,
> +	uintptr_t priv, const struct iio_chan_spec *chan, char *buf);
> +ssize_t iio_enum_read(struct iio_dev *indio_dev,
> +	uintptr_t priv, const struct iio_chan_spec *chan, char *buf);
> +ssize_t iio_enum_write(struct iio_dev *indio_dev,
> +	uintptr_t priv, const struct iio_chan_spec *chan, const char *buf,
> +	size_t len);
> +
> +/**
> + * IIO_ENUM() - Initialize enum extended channel attribute
> + * @_name: Attribute name
> + * @_shared: Whether the attribute is shared between all channels
> + * @_e: Pointer to a iio_enum struct
> + *
> + * This should usually be used together with IIO_ENUM_AVAILABLE()
> + */
> +#define IIO_ENUM(_name, _shared, _e) \
> +{ \
> +	.name = (_name), \
> +	.shared = (_shared), \
> +	.read = iio_enum_read, \
> +	.write = iio_enum_write, \
> +	.private = (uintptr_t)(_e), \
> +}
> +
> +/**
> + * IIO_ENUM_AVAILABLE() - Initialize enum available extended channel attribute
> + * @_name: Attribute name ("_available" will be appended to the name)
> + * @_e: Pointer to a iio_enum struct
> + *
> + * Creates a read only attribute which list all the available enum items in a
> + * space separated list. This should usually be used together with IIO_ENUM()
> + */
> +#define IIO_ENUM_AVAILABLE(_name, _e) \
> +{ \
> +	.name = (_name "_available"), \
> +	.shared = true, \
> +	.read = iio_enum_available_read, \
> +	.private = (uintptr_t)(_e), \
> +}
> +
> +/**
>   * struct iio_chan_spec - specification of a single channel
>   * @type:		What type of measurement is the channel making.
>   * @channel:		What number or name do we wish to assign the channel.