iio: core: Introduce iio_push_to_buffers_with_ts_unaligned()

Whilst it is almost always possible to arrange for scan data to be
read directly into a buffer that is suitable for passing to
iio_push_to_buffers_with_timestamp(), there are a few places where
leading data needs to be skipped over.

For these cases introduce a function that will allocate an appropriate
sized and aligned bounce buffer (if not already allocated) and copy
the unaligned data into that before calling
iio_push_to_buffers_with_timestamp() on the bounce buffer.
We tie the lifespace of this buffer to that of the iio_dev.dev
which should ensure no memory leaks occur.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20210613151039.569883-2-jic23@kernel.org

drivers/iio/industrialio-buffer.c

@@ -1731,6 +1731,52 @@ int iio_push_to_buffers(struct iio_dev *indio_dev, const void *data)
 }
 EXPORT_SYMBOL_GPL(iio_push_to_buffers);
 
+/**
+ * iio_push_to_buffers_with_ts_unaligned() - push to registered buffer,
+ *    no alignment or space requirements.
+ * @indio_dev:		iio_dev structure for device.
+ * @data:		channel data excluding the timestamp.
+ * @data_sz:		size of data.
+ * @timestamp:		timestamp for the sample data.
+ *
+ * This special variant of iio_push_to_buffers_with_timestamp() does
+ * not require space for the timestamp, or 8 byte alignment of data.
+ * It does however require an allocation on first call and additional
+ * copies on all calls, so should be avoided if possible.
+ */
+int iio_push_to_buffers_with_ts_unaligned(struct iio_dev *indio_dev,
+					  const void *data,
+					  size_t data_sz,
+					  int64_t timestamp)
+{
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+
+	/*
+	 * Conservative estimate - we can always safely copy the minimum
+	 * of either the data provided or the length of the destination buffer.
+	 * This relaxed limit allows the calling drivers to be lax about
+	 * tracking the size of the data they are pushing, at the cost of
+	 * unnecessary copying of padding.
+	 */
+	data_sz = min_t(size_t, indio_dev->scan_bytes, data_sz);
+	if (iio_dev_opaque->bounce_buffer_size !=  indio_dev->scan_bytes) {
+		void *bb;
+
+		bb = devm_krealloc(&indio_dev->dev,
+				   iio_dev_opaque->bounce_buffer,
+				   indio_dev->scan_bytes, GFP_KERNEL);
+		if (!bb)
+			return -ENOMEM;
+		iio_dev_opaque->bounce_buffer = bb;
+		iio_dev_opaque->bounce_buffer_size = indio_dev->scan_bytes;
+	}
+	memcpy(iio_dev_opaque->bounce_buffer, data, data_sz);
+	return iio_push_to_buffers_with_timestamp(indio_dev,
+						  iio_dev_opaque->bounce_buffer,
+						  timestamp);
+}
+EXPORT_SYMBOL_GPL(iio_push_to_buffers_with_ts_unaligned);
+
 /**
  * iio_buffer_release() - Free a buffer's resources
  * @ref: Pointer to the kref embedded in the iio_buffer struct

include/linux/iio/buffer.h

@@ -38,6 +38,10 @@ static inline int iio_push_to_buffers_with_timestamp(struct iio_dev *indio_dev,
 	return iio_push_to_buffers(indio_dev, data);
 }
 
+int iio_push_to_buffers_with_ts_unaligned(struct iio_dev *indio_dev,
+					  const void *data, size_t data_sz,
+					  int64_t timestamp);
+
 bool iio_validate_scan_mask_onehot(struct iio_dev *indio_dev,
 				   const unsigned long *mask);
 

include/linux/iio/iio-opaque.h

@@ -23,6 +23,8 @@
  * @groupcounter:		index of next attribute group
  * @legacy_scan_el_group:	attribute group for legacy scan elements attribute group
  * @legacy_buffer_group:	attribute group for legacy buffer attributes group
+ * @bounce_buffer:		for devices that call iio_push_to_buffers_with_timestamp_unaligned()
+ * @bounce_buffer_size:		size of currently allocate bounce buffer
  * @scan_index_timestamp:	cache of the index to the timestamp
  * @clock_id:			timestamping clock posix identifier
  * @chrdev:			associated character device
@@ -50,6 +52,8 @@ struct iio_dev_opaque {
 	int				groupcounter;
 	struct attribute_group		legacy_scan_el_group;
 	struct attribute_group		legacy_buffer_group;
+	void				*bounce_buffer;
+	size_t				bounce_buffer_size;
 
 	unsigned int			scan_index_timestamp;
 	clockid_t			clock_id;