iio: core: rework iio device group creation

Up until now, the device groups that an IIO device had were limited to 6.
Two of these groups would account for buffer attributes (the buffer/ and
scan_elements/ directories).

Since we want to add multiple buffers per IIO device, this number may not
be enough, when adding a second buffer. So, this change reallocates the
groups array whenever an IIO device group is added, via a
iio_device_register_sysfs_group() helper.

This also means that the groups array should be assigned to
'indio_dev.dev.groups' really late, right before {cdev_}device_add() is
called to do the entire setup.
And we also must take care to free this array when the sysfs resources are
being cleaned up.

With this change we can also move the 'groups' & 'groupcounter' fields to
the iio_dev_opaque object. Up until now, this didn't make a whole lot of
sense (especially since we weren't sure how multibuffer support would look
like in the end).
But doing it now kills one birds with one stone.

An alternative, would be to add a configurable Kconfig symbol
CONFIG_IIO_MAX_BUFFERS_PER_DEVICE (or something like that) and compute a
static maximum of the groups we can support per IIO device. But that would
probably annoy a few people since that would make the system less
configurable.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210215104043.91251-11-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/iio_core.h

@@ -46,6 +46,9 @@ int __iio_add_chan_devattr(const char *postfix,
 			   struct list_head *attr_list);
 void iio_free_chan_devattr_list(struct list_head *attr_list);
 
+int iio_device_register_sysfs_group(struct iio_dev *indio_dev,
+				    const struct attribute_group *group);
+
 ssize_t iio_format_value(char *buf, unsigned int type, int size, int *vals);
 
 /* Event interface flags */

drivers/iio/industrialio-buffer.c

@@ -1287,7 +1287,9 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
 	buffer->buffer_group.name = "buffer";
 	buffer->buffer_group.attrs = attr;
 
-	indio_dev->groups[indio_dev->groupcounter++] = &buffer->buffer_group;
+	ret = iio_device_register_sysfs_group(indio_dev, &buffer->buffer_group);
+	if (ret)
+		goto error_free_buffer_attrs;
 
 	attrcount = 0;
 	INIT_LIST_HEAD(&buffer->scan_el_dev_attr_list);
@@ -1330,14 +1332,20 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
 
 	list_for_each_entry(p, &buffer->scan_el_dev_attr_list, l)
 		buffer->scan_el_group.attrs[attrn++] = &p->dev_attr.attr;
-	indio_dev->groups[indio_dev->groupcounter++] = &buffer->scan_el_group;
+
+	ret = iio_device_register_sysfs_group(indio_dev, &buffer->scan_el_group);
+	if (ret)
+		goto error_free_scan_el_attrs;
 
 	return 0;
 
+error_free_scan_el_attrs:
+	kfree(buffer->scan_el_group.attrs);
 error_free_scan_mask:
 	bitmap_free(buffer->scan_mask);
 error_cleanup_dynamic:
 	iio_free_chan_devattr_list(&buffer->scan_el_dev_attr_list);
+error_free_buffer_attrs:
 	kfree(buffer->buffer_group.attrs);
 
 	return ret;

drivers/iio/industrialio-core.c

@@ -1454,6 +1454,25 @@ static ssize_t iio_store_timestamp_clock(struct device *dev,
 	return len;
 }
 
+int iio_device_register_sysfs_group(struct iio_dev *indio_dev,
+				    const struct attribute_group *group)
+{
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+	const struct attribute_group **new, **old = iio_dev_opaque->groups;
+	unsigned int cnt = iio_dev_opaque->groupcounter;
+
+	new = krealloc(old, sizeof(*new) * (cnt + 2), GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	new[iio_dev_opaque->groupcounter++] = group;
+	new[iio_dev_opaque->groupcounter] = NULL;
+
+	iio_dev_opaque->groups = new;
+
+	return 0;
+}
+
 static DEVICE_ATTR(current_timestamp_clock, S_IRUGO | S_IWUSR,
 		   iio_show_timestamp_clock, iio_store_timestamp_clock);
 
@@ -1527,8 +1546,10 @@ static int iio_device_register_sysfs(struct iio_dev *indio_dev)
 	if (clk)
 		iio_dev_opaque->chan_attr_group.attrs[attrn++] = clk;
 
-	indio_dev->groups[indio_dev->groupcounter++] =
-		&iio_dev_opaque->chan_attr_group;
+	ret = iio_device_register_sysfs_group(indio_dev,
+					      &iio_dev_opaque->chan_attr_group);
+	if (ret)
+		goto error_clear_attrs;
 
 	return 0;
 
@@ -1545,6 +1566,7 @@ static void iio_device_unregister_sysfs(struct iio_dev *indio_dev)
 	iio_free_chan_devattr_list(&iio_dev_opaque->channel_attr_list);
 	kfree(iio_dev_opaque->chan_attr_group.attrs);
 	iio_dev_opaque->chan_attr_group.attrs = NULL;
+	kfree(iio_dev_opaque->groups);
 }
 
 static void iio_dev_release(struct device *device)
@@ -1594,7 +1616,6 @@ struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)
 		ALIGN(sizeof(struct iio_dev_opaque), IIO_ALIGN);
 
 	dev->dev.parent = parent;
-	dev->dev.groups = dev->groups;
 	dev->dev.type = &iio_device_type;
 	dev->dev.bus = &iio_bus_type;
 	device_initialize(&dev->dev);
@@ -1857,6 +1878,9 @@ int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
 		indio_dev->chrdev.owner = this_mod;
 	}
 
+	/* assign device groups now; they should be all registered now */
+	indio_dev->dev.groups = iio_dev_opaque->groups;
+
 	ret = cdev_device_add(&indio_dev->chrdev, &indio_dev->dev);
 	if (ret < 0)
 		goto error_unreg_eventset;

drivers/iio/industrialio-event.c

@@ -544,7 +544,10 @@ int iio_device_register_eventset(struct iio_dev *indio_dev)
 	/* Add all elements from the list. */
 	list_for_each_entry(p, &ev_int->dev_attr_list, l)
 		ev_int->group.attrs[attrn++] = &p->dev_attr.attr;
-	indio_dev->groups[indio_dev->groupcounter++] = &ev_int->group;
+
+	ret = iio_device_register_sysfs_group(indio_dev, &ev_int->group);
+	if (ret)
+		goto error_free_setup_event_lines;
 
 	ev_int->ioctl_handler.ioctl = iio_event_ioctl;
 	iio_device_ioctl_handler_register(&iio_dev_opaque->indio_dev,

drivers/iio/industrialio-trigger.c

@@ -694,10 +694,8 @@ EXPORT_SYMBOL(iio_trigger_validate_own_device);
 
 int iio_device_register_trigger_consumer(struct iio_dev *indio_dev)
 {
-	indio_dev->groups[indio_dev->groupcounter++] =
-		&iio_trigger_consumer_attr_group;
-
-	return 0;
+	return iio_device_register_sysfs_group(indio_dev,
+					       &iio_trigger_consumer_attr_group);
 }
 
 void iio_device_unregister_trigger_consumer(struct iio_dev *indio_dev)

include/linux/iio/iio-opaque.h

@@ -12,6 +12,8 @@
  *				attributes
  * @chan_attr_group:		group for all attrs in base directory
  * @ioctl_handlers:		ioctl handlers registered with the core handler
+ * @groups:			attribute groups
+ * @groupcounter:		index of next attribute group
  * @debugfs_dentry:		device specific debugfs dentry
  * @cached_reg_addr:		cached register address for debugfs reads
  * @read_buf:			read buffer to be used for the initial reg read
@@ -24,6 +26,8 @@ struct iio_dev_opaque {
 	struct list_head		channel_attr_list;
 	struct attribute_group		chan_attr_group;
 	struct list_head		ioctl_handlers;
+	const struct attribute_group	**groups;
+	int				groupcounter;
 #if defined(CONFIG_DEBUG_FS)
 	struct dentry			*debugfs_dentry;
 	unsigned			cached_reg_addr;

include/linux/iio/iio.h

@@ -518,8 +518,6 @@ struct iio_buffer_setup_ops {
  * @setup_ops:		[DRIVER] callbacks to call before and after buffer
  *			enable/disable
  * @chrdev:		[INTERN] associated character device
- * @groups:		[INTERN] attribute groups
- * @groupcounter:	[INTERN] index of next attribute group
  * @flags:		[INTERN] file ops related flags including busy flag.
  * @priv:		[DRIVER] reference to driver's private information
  *			**MUST** be accessed **ONLY** via iio_priv() helper
@@ -556,9 +554,6 @@ struct iio_dev {
 	struct mutex			info_exist_lock;
 	const struct iio_buffer_setup_ops	*setup_ops;
 	struct cdev			chrdev;
-#define IIO_MAX_GROUPS 6
-	const struct attribute_group	*groups[IIO_MAX_GROUPS + 1];
-	int				groupcounter;
 
 	unsigned long			flags;
 	void				*priv;