iio: buffer-dmaengine: Report buffer length requirements

The dmaengine buffer has some length alignment requirements that can differ
from platform to platform. If the length alignment requirements are not met
unexpected behavior like dropping of samples can occur.

Currently these requirements are not reported and applications need to know
the requirements of the platform by some out-of-band means.

Add a new buffer attribute that reports the length alignment requirements
called `length_align_bytes`. The reported length alignment is in bytes that
means the buffer length alignment in sample sets depends on the number of
enabled channels and the bytes per channel. Applications using this
attribute to determine the buffer size requirements need to consider this.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/drivers/iio/buffer/industrialio-buffer-dmaengine.c b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
index e0b92f3dec0e..744abd7e1269 100644
--- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
+++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
@@ -13,6 +13,7 @@
 #include <linux/module.h>
 
 #include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
 #include <linux/iio/buffer.h>
 #include <linux/iio/buffer_impl.h>
 #include <linux/iio/buffer-dma.h>
@@ -126,6 +127,24 @@ static const struct iio_dma_buffer_ops iio_dmaengine_default_ops = {
 	.abort = iio_dmaengine_buffer_abort,
 };
 
+static ssize_t iio_dmaengine_buffer_get_length_align(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct dmaengine_buffer *dmaengine_buffer =
+		iio_buffer_to_dmaengine_buffer(indio_dev->buffer);
+
+	return sprintf(buf, "%u\n", dmaengine_buffer->align);
+}
+
+static IIO_DEVICE_ATTR(length_align_bytes, 0444,
+		       iio_dmaengine_buffer_get_length_align, NULL, 0);
+
+static const struct attribute *iio_dmaengine_buffer_attrs[] = {
+	&iio_dev_attr_length_align_bytes.dev_attr.attr,
+	NULL,
+};
+
 /**
  * iio_dmaengine_buffer_alloc() - Allocate new buffer which uses DMAengine
  * @dev: Parent device for the buffer
@@ -179,6 +198,8 @@ struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
 
 	iio_dma_buffer_init(&dmaengine_buffer->queue, chan->device->dev,
 		&iio_dmaengine_default_ops);
+	iio_buffer_set_attrs(&dmaengine_buffer->queue.buffer,
+		iio_dmaengine_buffer_attrs);
 
 	dmaengine_buffer->queue.buffer.access = &iio_dmaengine_buffer_ops;