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>

1 files changed, 27 insertions, 3 deletions

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 92efbc245098..924f3a167125 100644
--- a/drivers/iio/industrialio-core.c
+++ b/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;