[RFC PATCH 1/5] iio: Add output buffer support

[Alexandru Ardelean]

From: Lars-Peter Clausen <lars@xxxxxxxxxx>

Currently IIO only supports buffer mode for capture devices like ADCs. Add
support for buffered mode for output devices like DACs.

The output buffer implementation is analogous to the input buffer
implementation. Instead of using read() to get data from the buffer write()
is used to copy data into the buffer.

poll() with POLLOUT will wakeup if there is space available for more or
equal to the configured watermark of samples.

Drivers can remove data from a buffer using iio_buffer_remove_sample(), the
function can e.g. called from a trigger handler to write the data to
hardware.

A buffer can only be either a output buffer or an input, but not both. So,
for a device that has an ADC and DAC path, this will mean 2 IIO buffers
(one for each direction).

The direction of the buffer is decided by the new direction field of the
iio_buffer struct and should be set after allocating and before registering
it.

Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
---
 drivers/iio/industrialio-buffer.c | 110 ++++++++++++++++++++++++++++--
 include/linux/iio/buffer.h        |   7 ++
 include/linux/iio/buffer_impl.h   |  11 +++
 3 files changed, 124 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index a0d1ad86022f..6f4f5f5544f3 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -162,6 +162,69 @@ static ssize_t iio_buffer_read(struct file *filp, char __user *buf,
 	return ret;
 }
 
+static size_t iio_buffer_space_available(struct iio_buffer *buf)
+{
+	if (buf->access->space_available)
+		return buf->access->space_available(buf);
+
+	return SIZE_MAX;
+}
+
+static ssize_t iio_buffer_write(struct file *filp, const char __user *buf,
+				size_t n, loff_t *f_ps)
+{
+	struct iio_dev_buffer_pair *ib = filp->private_data;
+	struct iio_buffer *rb = ib->buffer;
+	struct iio_dev *indio_dev = ib->indio_dev;
+	DEFINE_WAIT_FUNC(wait, woken_wake_function);
+	size_t datum_size;
+	size_t to_wait;
+	int ret;
+
+	if (!rb || !rb->access->write)
+		return -EINVAL;
+
+	datum_size = rb->bytes_per_datum;
+
+	/*
+	 * If datum_size is 0 there will never be anything to read from the
+	 * buffer, so signal end of file now.
+	 */
+	if (!datum_size)
+		return 0;
+
+	if (filp->f_flags & O_NONBLOCK)
+		to_wait = 0;
+	else
+		to_wait = min_t(size_t, n / datum_size, rb->watermark);
+
+	add_wait_queue(&rb->pollq, &wait);
+	do {
+		if (!indio_dev->info) {
+			ret = -ENODEV;
+			break;
+		}
+
+		if (iio_buffer_space_available(rb) < to_wait) {
+			if (signal_pending(current)) {
+				ret = -ERESTARTSYS;
+				break;
+			}
+
+			wait_woken(&wait, TASK_INTERRUPTIBLE,
+				   MAX_SCHEDULE_TIMEOUT);
+			continue;
+		}
+
+		ret = rb->access->write(rb, n, buf);
+		if (ret == 0 && (filp->f_flags & O_NONBLOCK))
+			ret = -EAGAIN;
+	} while (ret == 0);
+	remove_wait_queue(&rb->pollq, &wait);
+
+	return ret;
+}
+
 /**
  * iio_buffer_poll() - poll the buffer to find out if it has data
  * @filp:	File structure pointer for device access
@@ -182,8 +245,19 @@ static __poll_t iio_buffer_poll(struct file *filp,
 		return 0;
 
 	poll_wait(filp, &rb->pollq, wait);
-	if (iio_buffer_ready(indio_dev, rb, rb->watermark, 0))
-		return EPOLLIN | EPOLLRDNORM;
+
+	switch (rb->direction) {
+	case IIO_BUFFER_DIRECTION_IN:
+		if (iio_buffer_ready(indio_dev, rb, rb->watermark, 0))
+			return EPOLLIN | EPOLLRDNORM;
+		break;
+	case IIO_BUFFER_DIRECTION_OUT:
+		if (iio_buffer_space_available(rb) >= rb->watermark)
+			return EPOLLOUT | EPOLLWRNORM;
+		break;
+	}
+
+	/* need a way of knowing if there may be enough data... */
 	return 0;
 }
 
@@ -232,6 +306,16 @@ void iio_buffer_wakeup_poll(struct iio_dev *indio_dev)
 	}
 }
 
+int iio_buffer_remove_sample(struct iio_buffer *buffer, u8 *data)
+{
+	if (!buffer || !buffer->access)
+		return -EINVAL;
+	if (!buffer->access->write)
+		return -ENOSYS;
+	return buffer->access->remove_from(buffer, data);
+}
+EXPORT_SYMBOL_GPL(iio_buffer_remove_sample);
+
 void iio_buffer_init(struct iio_buffer *buffer)
 {
 	INIT_LIST_HEAD(&buffer->demux_list);
@@ -803,6 +887,8 @@ static int iio_verify_update(struct iio_dev *indio_dev,
 	}
 
 	if (insert_buffer) {
+		if (insert_buffer->direction == IIO_BUFFER_DIRECTION_OUT)
+			strict_scanmask = true;
 		bitmap_or(compound_mask, compound_mask,
 			  insert_buffer->scan_mask, indio_dev->masklength);
 		scan_timestamp |= insert_buffer->scan_timestamp;
@@ -945,6 +1031,8 @@ static int iio_update_demux(struct iio_dev *indio_dev)
 	int ret;
 
 	list_for_each_entry(buffer, &iio_dev_opaque->buffer_list, buffer_list) {
+		if (buffer->direction == IIO_BUFFER_DIRECTION_OUT)
+			continue;
 		ret = iio_buffer_update_demux(indio_dev, buffer);
 		if (ret < 0)
 			goto error_clear_mux_table;
@@ -1155,6 +1243,11 @@ int iio_update_buffers(struct iio_dev *indio_dev,
 	mutex_lock(&indio_dev->info_exist_lock);
 	mutex_lock(&indio_dev->mlock);
 
+	if (insert_buffer->direction == IIO_BUFFER_DIRECTION_OUT) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
 	if (insert_buffer && iio_buffer_is_active(insert_buffer))
 		insert_buffer = NULL;
 
@@ -1400,6 +1493,7 @@ static const struct file_operations iio_buffer_chrdev_fileops = {
 	.owner = THIS_MODULE,
 	.llseek = noop_llseek,
 	.read = iio_buffer_read,
+	.write = iio_buffer_write,
 	.poll = iio_buffer_poll,
 	.unlocked_ioctl = iio_buffer_ioctl,
 	.compat_ioctl = compat_ptr_ioctl,
@@ -1914,8 +2008,16 @@ static int iio_buffer_mmap(struct file *filep, struct vm_area_struct *vma)
 	if (!(vma->vm_flags & VM_SHARED))
 		return -EINVAL;
 
-	if (!(vma->vm_flags & VM_READ))
-		return -EINVAL;
+	switch (buffer->direction) {
+	case IIO_BUFFER_DIRECTION_IN:
+		if (!(vma->vm_flags & VM_READ))
+			return -EINVAL;
+		break;
+	case IIO_BUFFER_DIRECTION_OUT:
+		if (!(vma->vm_flags & VM_WRITE))
+			return -EINVAL;
+		break;
+	}
 
 	return buffer->access->mmap(buffer, vma);
 }
diff --git a/include/linux/iio/buffer.h b/include/linux/iio/buffer.h
index b6928ac5c63d..e87b8773253d 100644
--- a/include/linux/iio/buffer.h
+++ b/include/linux/iio/buffer.h
@@ -11,8 +11,15 @@
 
 struct iio_buffer;
 
+enum iio_buffer_direction {
+	IIO_BUFFER_DIRECTION_IN,
+	IIO_BUFFER_DIRECTION_OUT,
+};
+
 int iio_push_to_buffers(struct iio_dev *indio_dev, const void *data);
 
+int iio_buffer_remove_sample(struct iio_buffer *buffer, u8 *data);
+
 /**
  * iio_push_to_buffers_with_timestamp() - push data and timestamp to buffers
  * @indio_dev:		iio_dev structure for device.
diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
index 1d57dc7ccb4f..47bdbf4a4519 100644
--- a/include/linux/iio/buffer_impl.h
+++ b/include/linux/iio/buffer_impl.h
@@ -7,6 +7,7 @@
 #ifdef CONFIG_IIO_BUFFER
 
 #include <uapi/linux/iio/buffer.h>
+#include <linux/iio/buffer.h>
 
 struct iio_dev;
 struct iio_buffer;
@@ -23,6 +24,10 @@ struct iio_buffer;
  * @read:		try to get a specified number of bytes (must exist)
  * @data_available:	indicates how much data is available for reading from
  *			the buffer.
+ * @remove_from:	remove sample from buffer. Drivers should calls this to
+ *			remove a sample from a buffer.
+ * @write:		try to write a number of bytes
+ * @space_available:	returns the amount of bytes available in a buffer
  * @request_update:	if a parameter change has been marked, update underlying
  *			storage.
  * @set_bytes_per_datum:set number of bytes per datum
@@ -61,6 +66,9 @@ struct iio_buffer_access_funcs {
 	int (*store_to)(struct iio_buffer *buffer, const void *data);
 	int (*read)(struct iio_buffer *buffer, size_t n, char __user *buf);
 	size_t (*data_available)(struct iio_buffer *buffer);
+	int (*remove_from)(struct iio_buffer *buffer, void *data);
+	int (*write)(struct iio_buffer *buffer, size_t n, const char __user *buf);
+	size_t (*space_available)(struct iio_buffer *buffer);
 
 	int (*request_update)(struct iio_buffer *buffer);
 
@@ -103,6 +111,9 @@ struct iio_buffer {
 	/**  @bytes_per_datum: Size of individual datum including timestamp. */
 	size_t bytes_per_datum;
 
+	/* @direction: Direction of the data stream (in/out). */
+	enum iio_buffer_direction direction;
+
 	/**
 	 * @access: Buffer access functions associated with the
 	 * implementation.
-- 
2.17.1