iio: add read scale and offset services to iio backend framework

Add iio_backend_read_scale() and iio_backend_read_offset() services
to read channel scale and offset from an IIO backbend device.

Also add a read_raw callback which replicates the read_raw callback of
the IIO framework, and is intended to request miscellaneous channel
attributes from the backend device.
Both scale and offset helpers use this callback.
Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240730084640.1307938-2-olivier.moysan@foss.st.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-backend.c

@@ -502,6 +502,25 @@ int devm_iio_backend_request_buffer(struct device *dev,
 }
 EXPORT_SYMBOL_NS_GPL(devm_iio_backend_request_buffer, IIO_BACKEND);
 
+/**
+ * iio_backend_read_raw - Read a channel attribute from a backend device.
+ * @back:	Backend device
+ * @chan:	IIO channel reference
+ * @val:	First returned value
+ * @val2:	Second returned value
+ * @mask:	Specify the attribute to return
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int iio_backend_read_raw(struct iio_backend *back,
+			 struct iio_chan_spec const *chan, int *val, int *val2,
+			 long mask)
+{
+	return iio_backend_op_call(back, read_raw, chan, val, val2, mask);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_read_raw, IIO_BACKEND);
+
 static struct iio_backend *iio_backend_from_indio_dev_parent(const struct device *dev)
 {
 	struct iio_backend *back = ERR_PTR(-ENODEV), *iter;

include/linux/iio/backend.h

@@ -3,6 +3,7 @@
 #define _IIO_BACKEND_H_
 
 #include <linux/types.h>
+#include <linux/iio/iio.h>
 
 struct iio_chan_spec;
 struct fwnode_handle;
@@ -85,6 +86,7 @@ enum iio_backend_sample_trigger {
  * @extend_chan_spec: Extend an IIO channel.
  * @ext_info_set: Extended info setter.
  * @ext_info_get: Extended info getter.
+ * @read_raw: Read a channel attribute from a backend device
  * @debugfs_print_chan_status: Print channel status into a buffer.
  * @debugfs_reg_access: Read or write register value of backend.
  **/
@@ -119,6 +121,9 @@ struct iio_backend_ops {
 			    const char *buf, size_t len);
 	int (*ext_info_get)(struct iio_backend *back, uintptr_t private,
 			    const struct iio_chan_spec *chan, char *buf);
+	int (*read_raw)(struct iio_backend *back,
+			struct iio_chan_spec const *chan, int *val, int *val2,
+			long mask);
 	int (*debugfs_print_chan_status)(struct iio_backend *back,
 					 unsigned int chan, char *buf,
 					 size_t len);
@@ -162,7 +167,9 @@ ssize_t iio_backend_ext_info_set(struct iio_dev *indio_dev, uintptr_t private,
 				 const char *buf, size_t len);
 ssize_t iio_backend_ext_info_get(struct iio_dev *indio_dev, uintptr_t private,
 				 const struct iio_chan_spec *chan, char *buf);
-
+int iio_backend_read_raw(struct iio_backend *back,
+			 struct iio_chan_spec const *chan, int *val, int *val2,
+			 long mask);
 int iio_backend_extend_chan_spec(struct iio_backend *back,
 				 struct iio_chan_spec *chan);
 void *iio_backend_get_priv(const struct iio_backend *conv);
@@ -174,6 +181,21 @@ __devm_iio_backend_get_from_fwnode_lookup(struct device *dev,
 int devm_iio_backend_register(struct device *dev,
 			      const struct iio_backend_info *info, void *priv);
 
+static inline int iio_backend_read_scale(struct iio_backend *back,
+					 struct iio_chan_spec const *chan,
+					 int *val, int *val2)
+{
+	return iio_backend_read_raw(back, chan, val, val2, IIO_CHAN_INFO_SCALE);
+}
+
+static inline int iio_backend_read_offset(struct iio_backend *back,
+					  struct iio_chan_spec const *chan,
+					  int *val, int *val2)
+{
+	return iio_backend_read_raw(back, chan, val, val2,
+				    IIO_CHAN_INFO_OFFSET);
+}
+
 ssize_t iio_backend_debugfs_print_chan_status(struct iio_backend *back,
 					      unsigned int chan, char *buf,
 					      size_t len);