Add support for IIO devices in ASoC

Merge series from Herve Codina <herve.codina@bootlin.com>:

Several weeks ago, I sent a series [1] for adding a potentiometer as an
auxiliary device in ASoC. The feedback was that the potentiometer should
be directly handled in IIO (as other potentiometers) and something more
generic should be present in ASoC in order to have a binding to import
some IIO devices into sound cards.

The series related to the IIO potentiometer device is already applied.

This series introduces audio-iio-aux. Its goal is to offer the binding
between IIO and ASoC.
It exposes attached IIO devices as ASoC auxiliary devices and allows to
control them through mixer controls.

On my system, the IIO device is a potentiometer and it is present in an
amplifier design present in the audio path.

2 files changed, 91 insertions, 10 deletions

diff --git a/include/linux/iio/consumer.h b/include/linux/iio/consumer.h
index 6802596b017c..e9910b41d48e 100644
--- a/include/linux/iio/consumer.h
+++ b/include/linux/iio/consumer.h
@@ -201,8 +201,9 @@ struct iio_dev
  * @chan:		The channel being queried.
  * @val:		Value read back.
  *
- * Note raw reads from iio channels are in adc counts and hence
- * scale will need to be applied if standard units required.
+ * Note, if standard units are required, raw reads from iio channels
+ * need the offset (default 0) and scale (default 1) to be applied
+ * as (raw + offset) * scale.
  */
 int iio_read_channel_raw(struct iio_channel *chan,
 			 int *val);
@@ -212,8 +213,9 @@ int iio_read_channel_raw(struct iio_channel *chan,
  * @chan:		The channel being queried.
  * @val:		Value read back.
  *
- * Note raw reads from iio channels are in adc counts and hence
- * scale will need to be applied if standard units required.
+ * Note, if standard units are required, raw reads from iio channels
+ * need the offset (default 0) and scale (default 1) to be applied
+ * as (raw + offset) * scale.
  *
  * In opposit to the normal iio_read_channel_raw this function
  * returns the average of multiple reads.
@@ -281,8 +283,9 @@ int iio_read_channel_attribute(struct iio_channel *chan, int *val,
  * @chan:		The channel being queried.
  * @val:		Value being written.
  *
- * Note raw writes to iio channels are in dac counts and hence
- * scale will need to be applied if standard units required.
+ * Note that for raw writes to iio channels, if the value provided is
+ * in standard units, the affect of the scale and offset must be removed
+ * as (value / scale) - offset.
  */
 int iio_write_channel_raw(struct iio_channel *chan, int val);
 
@@ -292,12 +295,25 @@ int iio_write_channel_raw(struct iio_channel *chan, int val);
  * @chan:		The channel being queried.
  * @val:		Value read back.
  *
- * Note raw reads from iio channels are in adc counts and hence
- * scale will need to be applied if standard units are required.
+ * Note, if standard units are required, raw reads from iio channels
+ * need the offset (default 0) and scale (default 1) to be applied
+ * as (raw + offset) * scale.
  */
 int iio_read_max_channel_raw(struct iio_channel *chan, int *val);
 
 /**
+ * iio_read_min_channel_raw() - read minimum available raw value from a given
+ *				channel, i.e. the minimum possible value.
+ * @chan:		The channel being queried.
+ * @val:		Value read back.
+ *
+ * Note, if standard units are required, raw reads from iio channels
+ * need the offset (default 0) and scale (default 1) to be applied
+ * as (raw + offset) * scale.
+ */
+int iio_read_min_channel_raw(struct iio_channel *chan, int *val);
+
+/**
  * iio_read_avail_channel_raw() - read available raw values from a given channel
  * @chan:		The channel being queried.
  * @vals:		Available values read back.
@@ -308,8 +324,9 @@ int iio_read_max_channel_raw(struct iio_channel *chan, int *val);
  * For ranges, three vals are always returned; min, step and max.
  * For lists, all the possible values are enumerated.
  *
- * Note raw available values from iio channels are in adc counts and
- * hence scale will need to be applied if standard units are required.
+ * Note, if standard units are required, raw available values from iio
+ * channels need the offset (default 0) and scale (default 1) to be applied
+ * as (raw + offset) * scale.
  */
 int iio_read_avail_channel_raw(struct iio_channel *chan,
 			       const int **vals, int *length);
diff --git a/include/linux/minmax.h b/include/linux/minmax.h
index 396df1121bff..798c6963909f 100644
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -133,6 +133,70 @@
  */
 #define max_t(type, x, y)	__careful_cmp((type)(x), (type)(y), >)
 
+/*
+ * Remove a const qualifier from integer types
+ * _Generic(foo, type-name: association, ..., default: association) performs a
+ * comparison against the foo type (not the qualified type).
+ * Do not use the const keyword in the type-name as it will not match the
+ * unqualified type of foo.
+ */
+#define __unconst_integer_type_cases(type)	\
+	unsigned type:  (unsigned type)0,	\
+	signed type:    (signed type)0
+
+#define __unconst_integer_typeof(x) typeof(			\
+	_Generic((x),						\
+		char: (char)0,					\
+		__unconst_integer_type_cases(char),		\
+		__unconst_integer_type_cases(short),		\
+		__unconst_integer_type_cases(int),		\
+		__unconst_integer_type_cases(long),		\
+		__unconst_integer_type_cases(long long),	\
+		default: (x)))
+
+/*
+ * Do not check the array parameter using __must_be_array().
+ * In the following legit use-case where the "array" passed is a simple pointer,
+ * __must_be_array() will return a failure.
+ * --- 8< ---
+ * int *buff
+ * ...
+ * min = min_array(buff, nb_items);
+ * --- 8< ---
+ *
+ * The first typeof(&(array)[0]) is needed in order to support arrays of both
+ * 'int *buff' and 'int buff[N]' types.
+ *
+ * The array can be an array of const items.
+ * typeof() keeps the const qualifier. Use __unconst_integer_typeof() in order
+ * to discard the const qualifier for the __element variable.
+ */
+#define __minmax_array(op, array, len) ({				\
+	typeof(&(array)[0]) __array = (array);				\
+	typeof(len) __len = (len);					\
+	__unconst_integer_typeof(__array[0]) __element = __array[--__len]; \
+	while (__len--)							\
+		__element = op(__element, __array[__len]);		\
+	__element; })
+
+/**
+ * min_array - return minimum of values present in an array
+ * @array: array
+ * @len: array length
+ *
+ * Note that @len must not be zero (empty array).
+ */
+#define min_array(array, len) __minmax_array(min, array, len)
+
+/**
+ * max_array - return maximum of values present in an array
+ * @array: array
+ * @len: array length
+ *
+ * Note that @len must not be zero (empty array).
+ */
+#define max_array(array, len) __minmax_array(max, array, len)
+
 /**
  * clamp_t - return a value clamped to a given range using a given type
  * @type: the type of variable to use