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SubjectRe: [PATCH v3 10/11] iio: buffer: introduce support for attaching more IIO buffers
On Mon, 1 Feb 2021 16:51:04 +0200
Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:

> With this change, calling iio_device_attach_buffer() will actually attach
> more buffers.
> Right now this doesn't do any validation of whether a buffer is attached
> twice; maybe that can be added later (if needed). Attaching a buffer more
> than once should yield noticeably bad results.
>
> The first buffer is the legacy buffer, so a reference is kept to it.
>
> At this point, accessing the data for the extra buffers (that are added
> after the first one) isn't possible yet.
>
> The iio_device_attach_buffer() is also changed to return an error code,
> which for now is -ENOMEM if the array could not be realloc-ed for more
> buffers.
>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
A few minor comments inline.

Thanks,

J
> ---
> drivers/iio/industrialio-buffer.c | 80 +++++++++++++++++++++++++------
> include/linux/iio/buffer.h | 4 +-
> include/linux/iio/buffer_impl.h | 3 ++
> include/linux/iio/iio-opaque.h | 4 ++
> 4 files changed, 74 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 692f721588e2..a69bb705d173 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -1445,11 +1445,21 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
> return ret;
> }
>
> +static void __iio_buffer_free_sysfs_and_mask(struct iio_buffer *buffer)
> +{
> + bitmap_free(buffer->scan_mask);
> + kfree(buffer->buffer_group.name);
> + kfree(buffer->buffer_group.attrs);
> + iio_free_chan_devattr_list(&buffer->buffer_attr_list);
> +}
> +
> int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
> {
> + struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> struct iio_buffer *buffer = indio_dev->buffer;
> const struct iio_chan_spec *channels;
> - int i;
> + int unwind_idx;
> + int ret, i;
>
> channels = indio_dev->channels;
> if (channels) {
> @@ -1463,27 +1473,45 @@ int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
> if (!buffer)
> return 0;
>
> - return __iio_buffer_alloc_sysfs_and_mask(buffer, indio_dev, 0);
> -}
> + for (i = 0; i < iio_dev_opaque->attached_buffers_cnt; i++) {
> + buffer = iio_dev_opaque->attached_buffers[i];
> + ret = __iio_buffer_alloc_sysfs_and_mask(buffer, indio_dev, i);
> + if (ret) {
> + unwind_idx = i;
Gut feeling would be to use i instead of introducing unwind_idx, but it
doesn't really matter if you prefer this.

> + goto error_unwind_sysfs_and_mask;
> + }
> + }
>
> -static void __iio_buffer_free_sysfs_and_mask(struct iio_buffer *buffer)
> -{
> - bitmap_free(buffer->scan_mask);
> - kfree(buffer->buffer_group.name);
> - kfree(buffer->buffer_group.attrs);
> - iio_free_chan_devattr_list(&buffer->buffer_attr_list);

could you put this move in a precursor patch. It's making a mess
of the diff and hence this harder to review than it should be.

> + return 0;
> +
> +error_unwind_sysfs_and_mask:
> + for (; unwind_idx >= 0; unwind_idx--) {
> + buffer = iio_dev_opaque->attached_buffers[unwind_idx];
> + __iio_buffer_free_sysfs_and_mask(buffer);
> + }
> + kfree(iio_dev_opaque->attached_buffers);
> + iio_dev_opaque->attached_buffers = NULL;
> + return ret;
> }
>
> void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
> {
> + struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> struct iio_buffer *buffer = indio_dev->buffer;
> + int i;
>
> if (!buffer)
> return;
>
> iio_buffer_unregister_legacy_sysfs_groups(indio_dev);
>
> - __iio_buffer_free_sysfs_and_mask(buffer);
> + for (i = iio_dev_opaque->attached_buffers_cnt - 1; i >= 0; i--) {
> + buffer = iio_dev_opaque->attached_buffers[i];
> + __iio_buffer_free_sysfs_and_mask(buffer);
> + }
> +
> + kfree(iio_dev_opaque->attached_buffers);
> + iio_dev_opaque->attached_buffers = NULL;

For places where we set freed pointers to NULL, I'd like a comment on why.
Usually it makes me a bit worried we are doing something less than tidy.

> }
>
> /**
> @@ -1601,13 +1629,35 @@ EXPORT_SYMBOL_GPL(iio_buffer_put);
> * @indio_dev: The device the buffer should be attached to
> * @buffer: The buffer to attach to the device
> *
> + * Return 0 if successful, negative if error.
> + *
> * This function attaches a buffer to a IIO device. The buffer stays attached to
> - * the device until the device is freed. The function should only be called at
> - * most once per device.
> + * the device until the device is freed. For legacy reasons, the first attached
> + * buffer will also be assigned to 'indio_dev->buffer'.
> */
> -void iio_device_attach_buffer(struct iio_dev *indio_dev,
> - struct iio_buffer *buffer)
> +int iio_device_attach_buffer(struct iio_dev *indio_dev,
> + struct iio_buffer *buffer)
> {
> - indio_dev->buffer = iio_buffer_get(buffer);
> + struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> + struct iio_buffer **new, **old = iio_dev_opaque->attached_buffers;
> + unsigned int cnt = iio_dev_opaque->attached_buffers_cnt;
> +
> + cnt++;
> +
> + new = krealloc(old, sizeof(*new) * cnt, GFP_KERNEL);
> + if (!new)
> + return -ENOMEM;
> + iio_dev_opaque->attached_buffers = new;
> +
> + buffer = iio_buffer_get(buffer);
> +
> + /* first buffer is legacy; attach it to the IIO device directly */
> + if (!indio_dev->buffer)
> + indio_dev->buffer = buffer;
> +
> + iio_dev_opaque->attached_buffers[cnt - 1] = buffer;
> + iio_dev_opaque->attached_buffers_cnt = cnt;
> +
> + return 0;
> }
> EXPORT_SYMBOL_GPL(iio_device_attach_buffer);
> diff --git a/include/linux/iio/buffer.h b/include/linux/iio/buffer.h
> index 8febc23f5f26..b6928ac5c63d 100644
> --- a/include/linux/iio/buffer.h
> +++ b/include/linux/iio/buffer.h
> @@ -41,7 +41,7 @@ static inline int iio_push_to_buffers_with_timestamp(struct iio_dev *indio_dev,
> bool iio_validate_scan_mask_onehot(struct iio_dev *indio_dev,
> const unsigned long *mask);
>
> -void iio_device_attach_buffer(struct iio_dev *indio_dev,
> - struct iio_buffer *buffer);
> +int iio_device_attach_buffer(struct iio_dev *indio_dev,
> + struct iio_buffer *buffer);
>
> #endif /* _IIO_BUFFER_GENERIC_H_ */
> diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
> index 41044320e581..768b90c64412 100644
> --- a/include/linux/iio/buffer_impl.h
> +++ b/include/linux/iio/buffer_impl.h
> @@ -112,6 +112,9 @@ struct iio_buffer {
> /* @demux_bounce: Buffer for doing gather from incoming scan. */
> void *demux_bounce;
>
> + /* @attached_entry: Entry in the devices list of buffers attached by the driver. */
> + struct list_head attached_entry;
> +
> /* @buffer_list: Entry in the devices list of current buffers. */
> struct list_head buffer_list;
>
> diff --git a/include/linux/iio/iio-opaque.h b/include/linux/iio/iio-opaque.h
> index 3e4c3cd248fd..c909835b6247 100644
> --- a/include/linux/iio/iio-opaque.h
> +++ b/include/linux/iio/iio-opaque.h
> @@ -7,6 +7,8 @@
> * struct iio_dev_opaque - industrial I/O device opaque information
> * @indio_dev: public industrial I/O device information
> * @event_interface: event chrdevs associated with interrupt lines
> + * @attached_buffers: array of buffers statically attached by the driver
> + * @attached_buffers_cnt: number of buffers in the array of statically attached buffers
> * @buffer_list: list of all buffers currently attached
> * @channel_attr_list: keep track of automatically created channel
> * attributes
> @@ -24,6 +26,8 @@
> struct iio_dev_opaque {
> struct iio_dev indio_dev;
> struct iio_event_interface *event_interface;
> + struct iio_buffer **attached_buffers;
> + unsigned int attached_buffers_cnt;
> struct list_head buffer_list;
> struct list_head channel_attr_list;
> struct attribute_group chan_attr_group;

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