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, 0 insertions, 5 deletions

diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index e4a9822e6495..f8585d01fc76 100644
--- a/include/linux/iio/iio.h
+++ b/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;