iio: add reference to iio buffer on iio_dev_attr

This change adds a reference to a 'struct iio_buffer' object on the
iio_dev_attr object. This way, we can use the created iio_dev_attr objects
on per-buffer basis (since they're allocated anyway).

A minor downside of this change is that the number of parameters on
__iio_add_chan_devattr() grows by 1. This looks like it could do with a bit
of a re-think.
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210215104043.91251-14-alexandru.ardelean@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/iio_core.h

@@ -12,6 +12,7 @@
 #include <linux/kernel.h>
 #include <linux/device.h>
 
+struct iio_buffer;
 struct iio_chan_spec;
 struct iio_dev;
 
@@ -43,6 +44,7 @@ int __iio_add_chan_devattr(const char *postfix,
 			   u64 mask,
 			   enum iio_shared_by shared_by,
 			   struct device *dev,
+			   struct iio_buffer *buffer,
 			   struct list_head *attr_list);
 void iio_free_chan_devattr_list(struct list_head *attr_list);
 

drivers/iio/industrialio-buffer.c

@@ -447,6 +447,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
 				     0,
 				     IIO_SEPARATE,
 				     &indio_dev->dev,
+				     buffer,
 				     &buffer->scan_el_dev_attr_list);
 	if (ret)
 		return ret;
@@ -458,6 +459,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
 				     0,
 				     0,
 				     &indio_dev->dev,
+				     buffer,
 				     &buffer->scan_el_dev_attr_list);
 	if (ret)
 		return ret;
@@ -470,6 +472,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
 					     chan->scan_index,
 					     0,
 					     &indio_dev->dev,
+					     buffer,
 					     &buffer->scan_el_dev_attr_list);
 	else
 		ret = __iio_add_chan_devattr("en",
@@ -479,6 +482,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
 					     chan->scan_index,
 					     0,
 					     &indio_dev->dev,
+					     buffer,
 					     &buffer->scan_el_dev_attr_list);
 	if (ret)
 		return ret;

drivers/iio/industrialio-core.c

@@ -1116,6 +1116,7 @@ int __iio_add_chan_devattr(const char *postfix,
 			   u64 mask,
 			   enum iio_shared_by shared_by,
 			   struct device *dev,
+			   struct iio_buffer *buffer,
 			   struct list_head *attr_list)
 {
 	int ret;
@@ -1131,6 +1132,7 @@ int __iio_add_chan_devattr(const char *postfix,
 		goto error_iio_dev_attr_free;
 	iio_attr->c = chan;
 	iio_attr->address = mask;
+	iio_attr->buffer = buffer;
 	list_for_each_entry(t, attr_list, l)
 		if (strcmp(t->dev_attr.attr.name,
 			   iio_attr->dev_attr.attr.name) == 0) {
@@ -1167,6 +1169,7 @@ static int iio_device_add_channel_label(struct iio_dev *indio_dev,
 				     0,
 				     IIO_SEPARATE,
 				     &indio_dev->dev,
+				     NULL,
 				     &iio_dev_opaque->channel_attr_list);
 	if (ret < 0)
 		return ret;
@@ -1192,6 +1195,7 @@ static int iio_device_add_info_mask_type(struct iio_dev *indio_dev,
 					     i,
 					     shared_by,
 					     &indio_dev->dev,
+					     NULL,
 					     &iio_dev_opaque->channel_attr_list);
 		if ((ret == -EBUSY) && (shared_by != IIO_SEPARATE))
 			continue;
@@ -1228,6 +1232,7 @@ static int iio_device_add_info_mask_type_avail(struct iio_dev *indio_dev,
 					     i,
 					     shared_by,
 					     &indio_dev->dev,
+					     NULL,
 					     &iio_dev_opaque->channel_attr_list);
 		kfree(avail_postfix);
 		if ((ret == -EBUSY) && (shared_by != IIO_SEPARATE))
@@ -1324,6 +1329,7 @@ static int iio_device_add_channel_sysfs(struct iio_dev *indio_dev,
 					i,
 					ext_info->shared,
 					&indio_dev->dev,
+					NULL,
 					&iio_dev_opaque->channel_attr_list);
 			i++;
 			if (ret == -EBUSY && ext_info->shared)

drivers/iio/industrialio-event.c

@@ -385,6 +385,7 @@ static int iio_device_add_event(struct iio_dev *indio_dev,
 
 		ret = __iio_add_chan_devattr(postfix, chan, show, store,
 			 (i << 16) | spec_index, shared_by, &indio_dev->dev,
+			 NULL,
 			&iio_dev_opaque->event_interface->dev_attr_list);
 		kfree(postfix);
 

include/linux/iio/sysfs.h

@@ -9,6 +9,7 @@
 #ifndef _INDUSTRIAL_IO_SYSFS_H_
 #define _INDUSTRIAL_IO_SYSFS_H_
 
+struct iio_buffer;
 struct iio_chan_spec;
 
 /**
@@ -17,12 +18,14 @@ struct iio_chan_spec;
  * @address:	associated register address
  * @l:		list head for maintaining list of dynamically created attrs
  * @c:		specification for the underlying channel
+ * @buffer:	the IIO buffer to which this attribute belongs to (if any)
  */
 struct iio_dev_attr {
 	struct device_attribute dev_attr;
 	u64 address;
 	struct list_head l;
 	struct iio_chan_spec const *c;
+	struct iio_buffer *buffer;
 };
 
 #define to_iio_dev_attr(_dev_attr)				\